From d34a16661ed0fed433c9469d7cfa3ca4d30ca42e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 14 Jun 2010 17:06:21 -0700 Subject: [PATCH 01/52] net: convert to rcu_dereference_index_check() The task_cls_classid() function applies rcu_dereference() to integers, which does not work with the shiny new sparse-based checking in rcu_dereference(). This commit therefore moves to the new RCU API rcu_dereference_index_check(). Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Acked-by: David S. Miller Acked-by: Herbert Xu --- include/net/cls_cgroup.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/net/cls_cgroup.h b/include/net/cls_cgroup.h index 726cc3536409..dd1fdb8293f5 100644 --- a/include/net/cls_cgroup.h +++ b/include/net/cls_cgroup.h @@ -45,7 +45,8 @@ static inline u32 task_cls_classid(struct task_struct *p) return 0; rcu_read_lock(); - id = rcu_dereference(net_cls_subsys_id); + id = rcu_dereference_index_check(net_cls_subsys_id, + rcu_read_lock_held()); if (id >= 0) classid = container_of(task_subsys_state(p, id), struct cgroup_cls_state, css)->classid; From ca5ecddfa8fcbd948c95530e7e817cee9fb43a3d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 28 Apr 2010 14:39:09 -0700 Subject: [PATCH 02/52] rcu: define __rcu address space modifier for sparse This commit provides definitions for the __rcu annotation defined earlier. This annotation permits sparse to check for correct use of RCU-protected pointers. If a pointer that is annotated with __rcu is accessed directly (as opposed to via rcu_dereference(), rcu_assign_pointer(), or one of their variants), sparse can be made to complain. To enable such complaints, use the new default-disabled CONFIG_SPARSE_RCU_POINTER kernel configuration option. Please note that these sparse complaints are intended to be a debugging aid, -not- a code-style-enforcement mechanism. There are special rcu_dereference_protected() and rcu_access_pointer() accessors for use when RCU read-side protection is not required, for example, when no other CPU has access to the data structure in question or while the current CPU hold the update-side lock. This patch also updates a number of docbook comments that were showing their age. Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Christopher Li Reviewed-by: Josh Triplett --- include/linux/compiler.h | 4 + include/linux/rcupdate.h | 358 +++++++++++++++++++++++---------------- include/linux/srcu.h | 27 ++- kernel/rcupdate.c | 6 +- lib/Kconfig.debug | 13 ++ 5 files changed, 260 insertions(+), 148 deletions(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index c1a62c56a660..320d6c94ff84 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -16,7 +16,11 @@ # define __release(x) __context__(x,-1) # define __cond_lock(x,c) ((c) ? ({ __acquire(x); 1; }) : 0) # define __percpu __attribute__((noderef, address_space(3))) +#ifdef CONFIG_SPARSE_RCU_POINTER +# define __rcu __attribute__((noderef, address_space(4))) +#else # define __rcu +#endif extern void __chk_user_ptr(const volatile void __user *); extern void __chk_io_ptr(const volatile void __iomem *); #else diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 9fbc54a2585d..b973dea2d6b0 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -41,6 +41,7 @@ #include #include #include +#include #ifdef CONFIG_RCU_TORTURE_TEST extern int rcutorture_runnable; /* for sysctl */ @@ -120,14 +121,15 @@ extern struct lockdep_map rcu_sched_lock_map; extern int debug_lockdep_rcu_enabled(void); /** - * rcu_read_lock_held - might we be in RCU read-side critical section? + * rcu_read_lock_held() - might we be in RCU read-side critical section? * * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, * this assumes we are in an RCU read-side critical section unless it can - * prove otherwise. + * prove otherwise. This is useful for debug checks in functions that + * require that they be called within an RCU read-side critical section. * - * Check debug_lockdep_rcu_enabled() to prevent false positives during boot + * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot * and while lockdep is disabled. */ static inline int rcu_read_lock_held(void) @@ -144,14 +146,16 @@ static inline int rcu_read_lock_held(void) extern int rcu_read_lock_bh_held(void); /** - * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section? + * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? * * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an * RCU-sched read-side critical section. In absence of * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side * critical section unless it can prove otherwise. Note that disabling * of preemption (including disabling irqs) counts as an RCU-sched - * read-side critical section. + * read-side critical section. This is useful for debug checks in functions + * that required that they be called within an RCU-sched read-side + * critical section. * * Check debug_lockdep_rcu_enabled() to prevent false positives during boot * and while lockdep is disabled. @@ -220,41 +224,155 @@ extern int rcu_my_thread_group_empty(void); } \ } while (0) +#else /* #ifdef CONFIG_PROVE_RCU */ + +#define __do_rcu_dereference_check(c) do { } while (0) + +#endif /* #else #ifdef CONFIG_PROVE_RCU */ + +/* + * Helper functions for rcu_dereference_check(), rcu_dereference_protected() + * and rcu_assign_pointer(). Some of these could be folded into their + * callers, but they are left separate in order to ease introduction of + * multiple flavors of pointers to match the multiple flavors of RCU + * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in + * the future. + */ +#define __rcu_access_pointer(p, space) \ + ({ \ + typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ + (void) (((typeof (*p) space *)p) == p); \ + ((typeof(*p) __force __kernel *)(_________p1)); \ + }) +#define __rcu_dereference_check(p, c, space) \ + ({ \ + typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ + __do_rcu_dereference_check(c); \ + (void) (((typeof (*p) space *)p) == p); \ + smp_read_barrier_depends(); \ + ((typeof(*p) __force __kernel *)(_________p1)); \ + }) +#define __rcu_dereference_protected(p, c, space) \ + ({ \ + __do_rcu_dereference_check(c); \ + (void) (((typeof (*p) space *)p) == p); \ + ((typeof(*p) __force __kernel *)(p)); \ + }) + +#define __rcu_dereference_index_check(p, c) \ + ({ \ + typeof(p) _________p1 = ACCESS_ONCE(p); \ + __do_rcu_dereference_check(c); \ + smp_read_barrier_depends(); \ + (_________p1); \ + }) +#define __rcu_assign_pointer(p, v, space) \ + ({ \ + if (!__builtin_constant_p(v) || \ + ((v) != NULL)) \ + smp_wmb(); \ + (p) = (typeof(*v) __force space *)(v); \ + }) + + /** - * rcu_dereference_check - rcu_dereference with debug checking + * rcu_access_pointer() - fetch RCU pointer with no dereferencing + * @p: The pointer to read + * + * Return the value of the specified RCU-protected pointer, but omit the + * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful + * when the value of this pointer is accessed, but the pointer is not + * dereferenced, for example, when testing an RCU-protected pointer against + * NULL. Although rcu_access_pointer() may also be used in cases where + * update-side locks prevent the value of the pointer from changing, you + * should instead use rcu_dereference_protected() for this use case. + */ +#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) + +/** + * rcu_dereference_check() - rcu_dereference with debug checking * @p: The pointer to read, prior to dereferencing * @c: The conditions under which the dereference will take place * * Do an rcu_dereference(), but check that the conditions under which the - * dereference will take place are correct. Typically the conditions indicate - * the various locking conditions that should be held at that point. The check - * should return true if the conditions are satisfied. + * dereference will take place are correct. Typically the conditions + * indicate the various locking conditions that should be held at that + * point. The check should return true if the conditions are satisfied. + * An implicit check for being in an RCU read-side critical section + * (rcu_read_lock()) is included. * * For example: * - * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() || - * lockdep_is_held(&foo->lock)); + * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); * * could be used to indicate to lockdep that foo->bar may only be dereferenced - * if either the RCU read lock is held, or that the lock required to replace + * if either rcu_read_lock() is held, or that the lock required to replace * the bar struct at foo->bar is held. * * Note that the list of conditions may also include indications of when a lock * need not be held, for example during initialisation or destruction of the * target struct: * - * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() || - * lockdep_is_held(&foo->lock) || + * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || * atomic_read(&foo->usage) == 0); + * + * Inserts memory barriers on architectures that require them + * (currently only the Alpha), prevents the compiler from refetching + * (and from merging fetches), and, more importantly, documents exactly + * which pointers are protected by RCU and checks that the pointer is + * annotated as __rcu. */ #define rcu_dereference_check(p, c) \ - ({ \ - __do_rcu_dereference_check(c); \ - rcu_dereference_raw(p); \ - }) + __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) /** - * rcu_dereference_protected - fetch RCU pointer when updates prevented + * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking + * @p: The pointer to read, prior to dereferencing + * @c: The conditions under which the dereference will take place + * + * This is the RCU-bh counterpart to rcu_dereference_check(). + */ +#define rcu_dereference_bh_check(p, c) \ + __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) + +/** + * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking + * @p: The pointer to read, prior to dereferencing + * @c: The conditions under which the dereference will take place + * + * This is the RCU-sched counterpart to rcu_dereference_check(). + */ +#define rcu_dereference_sched_check(p, c) \ + __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ + __rcu) + +#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ + +/** + * rcu_dereference_index_check() - rcu_dereference for indices with debug checking + * @p: The pointer to read, prior to dereferencing + * @c: The conditions under which the dereference will take place + * + * Similar to rcu_dereference_check(), but omits the sparse checking. + * This allows rcu_dereference_index_check() to be used on integers, + * which can then be used as array indices. Attempting to use + * rcu_dereference_check() on an integer will give compiler warnings + * because the sparse address-space mechanism relies on dereferencing + * the RCU-protected pointer. Dereferencing integers is not something + * that even gcc will put up with. + * + * Note that this function does not implicitly check for RCU read-side + * critical sections. If this function gains lots of uses, it might + * make sense to provide versions for each flavor of RCU, but it does + * not make sense as of early 2010. + */ +#define rcu_dereference_index_check(p, c) \ + __rcu_dereference_index_check((p), (c)) + +/** + * rcu_dereference_protected() - fetch RCU pointer when updates prevented + * @p: The pointer to read, prior to dereferencing + * @c: The conditions under which the dereference will take place * * Return the value of the specified RCU-protected pointer, but omit * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This @@ -263,35 +381,61 @@ extern int rcu_my_thread_group_empty(void); * prevent the compiler from repeating this reference or combining it * with other references, so it should not be used without protection * of appropriate locks. + * + * This function is only for update-side use. Using this function + * when protected only by rcu_read_lock() will result in infrequent + * but very ugly failures. */ #define rcu_dereference_protected(p, c) \ - ({ \ - __do_rcu_dereference_check(c); \ - (p); \ - }) - -#else /* #ifdef CONFIG_PROVE_RCU */ - -#define rcu_dereference_check(p, c) rcu_dereference_raw(p) -#define rcu_dereference_protected(p, c) (p) - -#endif /* #else #ifdef CONFIG_PROVE_RCU */ + __rcu_dereference_protected((p), (c), __rcu) /** - * rcu_access_pointer - fetch RCU pointer with no dereferencing + * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented + * @p: The pointer to read, prior to dereferencing + * @c: The conditions under which the dereference will take place * - * Return the value of the specified RCU-protected pointer, but omit the - * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful - * when the value of this pointer is accessed, but the pointer is not - * dereferenced, for example, when testing an RCU-protected pointer against - * NULL. This may also be used in cases where update-side locks prevent - * the value of the pointer from changing, but rcu_dereference_protected() - * is a lighter-weight primitive for this use case. + * This is the RCU-bh counterpart to rcu_dereference_protected(). */ -#define rcu_access_pointer(p) ACCESS_ONCE(p) +#define rcu_dereference_bh_protected(p, c) \ + __rcu_dereference_protected((p), (c), __rcu) /** - * rcu_read_lock - mark the beginning of an RCU read-side critical section. + * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented + * @p: The pointer to read, prior to dereferencing + * @c: The conditions under which the dereference will take place + * + * This is the RCU-sched counterpart to rcu_dereference_protected(). + */ +#define rcu_dereference_sched_protected(p, c) \ + __rcu_dereference_protected((p), (c), __rcu) + + +/** + * rcu_dereference() - fetch RCU-protected pointer for dereferencing + * @p: The pointer to read, prior to dereferencing + * + * This is a simple wrapper around rcu_dereference_check(). + */ +#define rcu_dereference(p) rcu_dereference_check(p, 0) + +/** + * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing + * @p: The pointer to read, prior to dereferencing + * + * Makes rcu_dereference_check() do the dirty work. + */ +#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) + +/** + * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing + * @p: The pointer to read, prior to dereferencing + * + * Makes rcu_dereference_check() do the dirty work. + */ +#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) + +/** + * rcu_read_lock() - mark the beginning of an RCU read-side critical section * * When synchronize_rcu() is invoked on one CPU while other CPUs * are within RCU read-side critical sections, then the @@ -337,7 +481,7 @@ static inline void rcu_read_lock(void) */ /** - * rcu_read_unlock - marks the end of an RCU read-side critical section. + * rcu_read_unlock() - marks the end of an RCU read-side critical section. * * See rcu_read_lock() for more information. */ @@ -349,15 +493,16 @@ static inline void rcu_read_unlock(void) } /** - * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section + * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section * * This is equivalent of rcu_read_lock(), but to be used when updates - * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks - * consider completion of a softirq handler to be a quiescent state, - * a process in RCU read-side critical section must be protected by - * disabling softirqs. Read-side critical sections in interrupt context - * can use just rcu_read_lock(). - * + * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since + * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a + * softirq handler to be a quiescent state, a process in RCU read-side + * critical section must be protected by disabling softirqs. Read-side + * critical sections in interrupt context can use just rcu_read_lock(), + * though this should at least be commented to avoid confusing people + * reading the code. */ static inline void rcu_read_lock_bh(void) { @@ -379,13 +524,12 @@ static inline void rcu_read_unlock_bh(void) } /** - * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section + * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section * - * Should be used with either - * - synchronize_sched() - * or - * - call_rcu_sched() and rcu_barrier_sched() - * on the write-side to insure proper synchronization. + * This is equivalent of rcu_read_lock(), but to be used when updates + * are being done using call_rcu_sched() or synchronize_rcu_sched(). + * Read-side critical sections can also be introduced by anything that + * disables preemption, including local_irq_disable() and friends. */ static inline void rcu_read_lock_sched(void) { @@ -420,54 +564,14 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) preempt_enable_notrace(); } - /** - * rcu_dereference_raw - fetch an RCU-protected pointer + * rcu_assign_pointer() - assign to RCU-protected pointer + * @p: pointer to assign to + * @v: value to assign (publish) * - * The caller must be within some flavor of RCU read-side critical - * section, or must be otherwise preventing the pointer from changing, - * for example, by holding an appropriate lock. This pointer may later - * be safely dereferenced. It is the caller's responsibility to have - * done the right thing, as this primitive does no checking of any kind. - * - * Inserts memory barriers on architectures that require them - * (currently only the Alpha), and, more importantly, documents - * exactly which pointers are protected by RCU. - */ -#define rcu_dereference_raw(p) ({ \ - typeof(p) _________p1 = ACCESS_ONCE(p); \ - smp_read_barrier_depends(); \ - (_________p1); \ - }) - -/** - * rcu_dereference - fetch an RCU-protected pointer, checking for RCU - * - * Makes rcu_dereference_check() do the dirty work. - */ -#define rcu_dereference(p) \ - rcu_dereference_check(p, rcu_read_lock_held()) - -/** - * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh - * - * Makes rcu_dereference_check() do the dirty work. - */ -#define rcu_dereference_bh(p) \ - rcu_dereference_check(p, rcu_read_lock_bh_held()) - -/** - * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched - * - * Makes rcu_dereference_check() do the dirty work. - */ -#define rcu_dereference_sched(p) \ - rcu_dereference_check(p, rcu_read_lock_sched_held()) - -/** - * rcu_assign_pointer - assign (publicize) a pointer to a newly - * initialized structure that will be dereferenced by RCU read-side - * critical sections. Returns the value assigned. + * Assigns the specified value to the specified RCU-protected + * pointer, ensuring that any concurrent RCU readers will see + * any prior initialization. Returns the value assigned. * * Inserts memory barriers on architectures that require them * (pretty much all of them other than x86), and also prevents @@ -476,14 +580,17 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) * call documents which pointers will be dereferenced by RCU read-side * code. */ - #define rcu_assign_pointer(p, v) \ - ({ \ - if (!__builtin_constant_p(v) || \ - ((v) != NULL)) \ - smp_wmb(); \ - (p) = (v); \ - }) + __rcu_assign_pointer((p), (v), __rcu) + +/** + * RCU_INIT_POINTER() - initialize an RCU protected pointer + * + * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep + * splats. + */ +#define RCU_INIT_POINTER(p, v) \ + p = (typeof(*v) __force __rcu *)(v) /* Infrastructure to implement the synchronize_() primitives. */ @@ -495,7 +602,7 @@ struct rcu_synchronize { extern void wakeme_after_rcu(struct rcu_head *head); /** - * call_rcu - Queue an RCU callback for invocation after a grace period. + * call_rcu() - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual update function to be invoked after the grace period * @@ -509,7 +616,7 @@ extern void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *head)); /** - * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. + * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual update function to be invoked after the grace period * @@ -566,37 +673,4 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head) } #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ -#ifndef CONFIG_PROVE_RCU -#define __do_rcu_dereference_check(c) do { } while (0) -#endif /* #ifdef CONFIG_PROVE_RCU */ - -#define __rcu_dereference_index_check(p, c) \ - ({ \ - typeof(p) _________p1 = ACCESS_ONCE(p); \ - __do_rcu_dereference_check(c); \ - smp_read_barrier_depends(); \ - (_________p1); \ - }) - -/** - * rcu_dereference_index_check() - rcu_dereference for indices with debug checking - * @p: The pointer to read, prior to dereferencing - * @c: The conditions under which the dereference will take place - * - * Similar to rcu_dereference_check(), but omits the sparse checking. - * This allows rcu_dereference_index_check() to be used on integers, - * which can then be used as array indices. Attempting to use - * rcu_dereference_check() on an integer will give compiler warnings - * because the sparse address-space mechanism relies on dereferencing - * the RCU-protected pointer. Dereferencing integers is not something - * that even gcc will put up with. - * - * Note that this function does not implicitly check for RCU read-side - * critical sections. If this function gains lots of uses, it might - * make sense to provide versions for each flavor of RCU, but it does - * not make sense as of early 2010. - */ -#define rcu_dereference_index_check(p, c) \ - __rcu_dereference_index_check((p), (c)) - #endif /* __LINUX_RCUPDATE_H */ diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 4d5d2f546dbf..6f456a720ff0 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -108,12 +108,31 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp) #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ /** - * srcu_dereference - fetch SRCU-protected pointer with checking + * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing + * @p: the pointer to fetch and protect for later dereferencing + * @sp: pointer to the srcu_struct, which is used to check that we + * really are in an SRCU read-side critical section. + * @c: condition to check for update-side use * - * Makes rcu_dereference_check() do the dirty work. + * If PROVE_RCU is enabled, invoking this outside of an RCU read-side + * critical section will result in an RCU-lockdep splat, unless @c evaluates + * to 1. The @c argument will normally be a logical expression containing + * lockdep_is_held() calls. */ -#define srcu_dereference(p, sp) \ - rcu_dereference_check(p, srcu_read_lock_held(sp)) +#define srcu_dereference_check(p, sp, c) \ + __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu) + +/** + * srcu_dereference - fetch SRCU-protected pointer for later dereferencing + * @p: the pointer to fetch and protect for later dereferencing + * @sp: pointer to the srcu_struct, which is used to check that we + * really are in an SRCU read-side critical section. + * + * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU + * is enabled, invoking this outside of an RCU read-side critical + * section will result in an RCU-lockdep splat. + */ +#define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0) /** * srcu_read_lock - register a new reader for an SRCU-protected structure. diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 4d169835fb36..6c79e851521c 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -73,12 +73,14 @@ int debug_lockdep_rcu_enabled(void) EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); /** - * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section? + * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? * * Check for bottom half being disabled, which covers both the * CONFIG_PROVE_RCU and not cases. Note that if someone uses * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) - * will show the situation. + * will show the situation. This is useful for debug checks in functions + * that require that they be called within an RCU read-side critical + * section. * * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. */ diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 1b4afd2e6ca0..12465f2ef766 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -539,6 +539,19 @@ config PROVE_RCU_REPEATEDLY disabling, allowing multiple RCU-lockdep warnings to be printed on a single reboot. +config SPARSE_RCU_POINTER + bool "RCU debugging: sparse-based checks for pointer usage" + default n + help + This feature enables the __rcu sparse annotation for + RCU-protected pointers. This annotation will cause sparse + to flag any non-RCU used of annotated pointers. This can be + helpful when debugging RCU usage. Please note that this feature + is not intended to enforce code cleanliness; it is instead merely + a debugging aid. + + Say Y to make sparse flag questionable use of RCU-protected pointers + Say N if you are unsure. config LOCKDEP From 67bdbffd696f29a0b68aa8daa285783a06651583 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Thu, 25 Feb 2010 16:55:13 +0100 Subject: [PATCH 03/52] rculist: avoid __rcu annotations This avoids warnings from missing __rcu annotations in the rculist implementation, making it possible to use the same lists in both RCU and non-RCU cases. We can add rculist annotations later, together with lockdep support for rculist, which is missing as well, but that may involve changing all the users. Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Pavel Emelyanov Cc: Sukadev Bhattiprolu Reviewed-by: Josh Triplett --- include/linux/rculist.h | 53 ++++++++++++++++++++++------------- include/linux/rculist_nulls.h | 16 +++++++---- kernel/pid.c | 2 +- 3 files changed, 46 insertions(+), 25 deletions(-) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 4ec3b38ce9c5..c10b1050dbe6 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -9,6 +9,12 @@ #include #include +/* + * return the ->next pointer of a list_head in an rcu safe + * way, we must not access it directly + */ +#define list_next_rcu(list) (*((struct list_head __rcu **)(&(list)->next))) + /* * Insert a new entry between two known consecutive entries. * @@ -20,7 +26,7 @@ static inline void __list_add_rcu(struct list_head *new, { new->next = next; new->prev = prev; - rcu_assign_pointer(prev->next, new); + rcu_assign_pointer(list_next_rcu(prev), new); next->prev = new; } @@ -138,7 +144,7 @@ static inline void list_replace_rcu(struct list_head *old, { new->next = old->next; new->prev = old->prev; - rcu_assign_pointer(new->prev->next, new); + rcu_assign_pointer(list_next_rcu(new->prev), new); new->next->prev = new; old->prev = LIST_POISON2; } @@ -193,7 +199,7 @@ static inline void list_splice_init_rcu(struct list_head *list, */ last->next = at; - rcu_assign_pointer(head->next, first); + rcu_assign_pointer(list_next_rcu(head), first); first->prev = head; at->prev = last; } @@ -208,7 +214,9 @@ static inline void list_splice_init_rcu(struct list_head *list, * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock(). */ #define list_entry_rcu(ptr, type, member) \ - container_of(rcu_dereference_raw(ptr), type, member) + ({typeof (*ptr) __rcu *__ptr = (typeof (*ptr) __rcu __force *)ptr; \ + container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member); \ + }) /** * list_first_entry_rcu - get the first element from a list @@ -225,9 +233,9 @@ static inline void list_splice_init_rcu(struct list_head *list, list_entry_rcu((ptr)->next, type, member) #define __list_for_each_rcu(pos, head) \ - for (pos = rcu_dereference_raw((head)->next); \ + for (pos = rcu_dereference_raw(list_next_rcu(head)); \ pos != (head); \ - pos = rcu_dereference_raw(pos->next)) + pos = rcu_dereference_raw(list_next_rcu((pos))) /** * list_for_each_entry_rcu - iterate over rcu list of given type @@ -257,9 +265,9 @@ static inline void list_splice_init_rcu(struct list_head *list, * as long as the traversal is guarded by rcu_read_lock(). */ #define list_for_each_continue_rcu(pos, head) \ - for ((pos) = rcu_dereference_raw((pos)->next); \ + for ((pos) = rcu_dereference_raw(list_next_rcu(pos)); \ prefetch((pos)->next), (pos) != (head); \ - (pos) = rcu_dereference_raw((pos)->next)) + (pos) = rcu_dereference_raw(list_next_rcu(pos))) /** * list_for_each_entry_continue_rcu - continue iteration over list of given type @@ -314,12 +322,19 @@ static inline void hlist_replace_rcu(struct hlist_node *old, new->next = next; new->pprev = old->pprev; - rcu_assign_pointer(*new->pprev, new); + rcu_assign_pointer(*(struct hlist_node __rcu **)new->pprev, new); if (next) new->next->pprev = &new->next; old->pprev = LIST_POISON2; } +/* + * return the first or the next element in an RCU protected hlist + */ +#define hlist_first_rcu(head) (*((struct hlist_node __rcu **)(&(head)->first))) +#define hlist_next_rcu(node) (*((struct hlist_node __rcu **)(&(node)->next))) +#define hlist_pprev_rcu(node) (*((struct hlist_node __rcu **)((node)->pprev))) + /** * hlist_add_head_rcu * @n: the element to add to the hash list. @@ -346,7 +361,7 @@ static inline void hlist_add_head_rcu(struct hlist_node *n, n->next = first; n->pprev = &h->first; - rcu_assign_pointer(h->first, n); + rcu_assign_pointer(hlist_first_rcu(h), n); if (first) first->pprev = &n->next; } @@ -374,7 +389,7 @@ static inline void hlist_add_before_rcu(struct hlist_node *n, { n->pprev = next->pprev; n->next = next; - rcu_assign_pointer(*(n->pprev), n); + rcu_assign_pointer(hlist_pprev_rcu(n), n); next->pprev = &n->next; } @@ -401,15 +416,15 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev, { n->next = prev->next; n->pprev = &prev->next; - rcu_assign_pointer(prev->next, n); + rcu_assign_pointer(hlist_next_rcu(prev), n); if (n->next) n->next->pprev = &n->next; } -#define __hlist_for_each_rcu(pos, head) \ - for (pos = rcu_dereference((head)->first); \ - pos && ({ prefetch(pos->next); 1; }); \ - pos = rcu_dereference(pos->next)) +#define __hlist_for_each_rcu(pos, head) \ + for (pos = rcu_dereference(hlist_first_rcu(head)); \ + pos && ({ prefetch(pos->next); 1; }); \ + pos = rcu_dereference(hlist_next_rcu(pos))) /** * hlist_for_each_entry_rcu - iterate over rcu list of given type @@ -422,11 +437,11 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev, * the _rcu list-mutation primitives such as hlist_add_head_rcu() * as long as the traversal is guarded by rcu_read_lock(). */ -#define hlist_for_each_entry_rcu(tpos, pos, head, member) \ - for (pos = rcu_dereference_raw((head)->first); \ +#define hlist_for_each_entry_rcu(tpos, pos, head, member) \ + for (pos = rcu_dereference_raw(hlist_first_rcu(head)); \ pos && ({ prefetch(pos->next); 1; }) && \ ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \ - pos = rcu_dereference_raw(pos->next)) + pos = rcu_dereference_raw(hlist_next_rcu(pos))) /** * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h index b70ffe53cb9f..2ae13714828b 100644 --- a/include/linux/rculist_nulls.h +++ b/include/linux/rculist_nulls.h @@ -37,6 +37,12 @@ static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n) } } +#define hlist_nulls_first_rcu(head) \ + (*((struct hlist_nulls_node __rcu __force **)&(head)->first)) + +#define hlist_nulls_next_rcu(node) \ + (*((struct hlist_nulls_node __rcu __force **)&(node)->next)) + /** * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization * @n: the element to delete from the hash list. @@ -88,7 +94,7 @@ static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n, n->next = first; n->pprev = &h->first; - rcu_assign_pointer(h->first, n); + rcu_assign_pointer(hlist_nulls_first_rcu(h), n); if (!is_a_nulls(first)) first->pprev = &n->next; } @@ -100,11 +106,11 @@ static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n, * @member: the name of the hlist_nulls_node within the struct. * */ -#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \ - for (pos = rcu_dereference_raw((head)->first); \ - (!is_a_nulls(pos)) && \ +#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \ + for (pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \ + (!is_a_nulls(pos)) && \ ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \ - pos = rcu_dereference_raw(pos->next)) + pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos))) #endif #endif diff --git a/kernel/pid.c b/kernel/pid.c index d55c6fb8d087..0f90c2f713f1 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -401,7 +401,7 @@ struct task_struct *pid_task(struct pid *pid, enum pid_type type) struct task_struct *result = NULL; if (pid) { struct hlist_node *first; - first = rcu_dereference_check(pid->tasks[type].first, + first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]), rcu_read_lock_held() || lockdep_tasklist_lock_is_held()); if (first) From 2c392b8c3450ceb69ba1b93cb0cddb3998fb8cdc Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Wed, 24 Feb 2010 19:41:39 +0100 Subject: [PATCH 04/52] cgroups: __rcu annotations Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Acked-by: Paul Menage Cc: Li Zefan Reviewed-by: Josh Triplett --- include/linux/cgroup.h | 4 ++-- include/linux/sched.h | 2 +- kernel/cgroup.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index ed3e92e41c6e..3cb7d04308cd 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -75,7 +75,7 @@ struct cgroup_subsys_state { unsigned long flags; /* ID for this css, if possible */ - struct css_id *id; + struct css_id __rcu *id; }; /* bits in struct cgroup_subsys_state flags field */ @@ -205,7 +205,7 @@ struct cgroup { struct list_head children; /* my children */ struct cgroup *parent; /* my parent */ - struct dentry *dentry; /* cgroup fs entry, RCU protected */ + struct dentry __rcu *dentry; /* cgroup fs entry, RCU protected */ /* Private pointers for each registered subsystem */ struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT]; diff --git a/include/linux/sched.h b/include/linux/sched.h index 1e2a6db2d7dd..bbffd087476c 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1418,7 +1418,7 @@ struct task_struct { #endif #ifdef CONFIG_CGROUPS /* Control Group info protected by css_set_lock */ - struct css_set *cgroups; + struct css_set __rcu *cgroups; /* cg_list protected by css_set_lock and tsk->alloc_lock */ struct list_head cg_list; #endif diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 192f88c5b0f9..e5c5497a7dca 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -138,7 +138,7 @@ struct css_id { * is called after synchronize_rcu(). But for safe use, css_is_removed() * css_tryget() should be used for avoiding race. */ - struct cgroup_subsys_state *css; + struct cgroup_subsys_state __rcu *css; /* * ID of this css. */ From 1b0ba1c9037b2265d6e5d0165d31e4c0269b603b Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Wed, 24 Feb 2010 19:45:09 +0100 Subject: [PATCH 05/52] credentials: rcu annotation Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Peter Zijlstra Cc: Ingo Molnar Acked-by: David Howells Reviewed-by: Josh Triplett --- include/linux/sched.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index bbffd087476c..2c756666c111 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1288,9 +1288,9 @@ struct task_struct { struct list_head cpu_timers[3]; /* process credentials */ - const struct cred *real_cred; /* objective and real subjective task + const struct cred __rcu *real_cred; /* objective and real subjective task * credentials (COW) */ - const struct cred *cred; /* effective (overridable) subjective task + const struct cred __rcu *cred; /* effective (overridable) subjective task * credentials (COW) */ struct mutex cred_guard_mutex; /* guard against foreign influences on * credential calculations From e63ba744a64d234c8a07c469ab1806443cb0a6ff Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Fri, 26 Feb 2010 18:01:20 +0100 Subject: [PATCH 06/52] keys: __rcu annotations Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Acked-by: David Howells Reviewed-by: Josh Triplett --- include/linux/cred.h | 2 +- include/linux/key.h | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/include/linux/cred.h b/include/linux/cred.h index 4d2c39573f36..4aaeab376446 100644 --- a/include/linux/cred.h +++ b/include/linux/cred.h @@ -84,7 +84,7 @@ struct thread_group_cred { atomic_t usage; pid_t tgid; /* thread group process ID */ spinlock_t lock; - struct key *session_keyring; /* keyring inherited over fork */ + struct key __rcu *session_keyring; /* keyring inherited over fork */ struct key *process_keyring; /* keyring private to this process */ struct rcu_head rcu; /* RCU deletion hook */ }; diff --git a/include/linux/key.h b/include/linux/key.h index cd50dfa1d4c2..3db0adce1fda 100644 --- a/include/linux/key.h +++ b/include/linux/key.h @@ -178,8 +178,9 @@ struct key { */ union { unsigned long value; + void __rcu *rcudata; void *data; - struct keyring_list *subscriptions; + struct keyring_list __rcu *subscriptions; } payload; }; From 5b22216e11f717adc344abc7f97b42e03127c6c0 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Wed, 3 Mar 2010 10:20:10 +0100 Subject: [PATCH 07/52] nfs: __rcu annotations Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Acked-by: Trond Myklebust --- include/linux/nfs_fs.h | 2 +- include/linux/sunrpc/auth_gss.h | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h index 508f8cf6da37..d0edf7d823ae 100644 --- a/include/linux/nfs_fs.h +++ b/include/linux/nfs_fs.h @@ -185,7 +185,7 @@ struct nfs_inode { struct nfs4_cached_acl *nfs4_acl; /* NFSv4 state */ struct list_head open_states; - struct nfs_delegation *delegation; + struct nfs_delegation __rcu *delegation; fmode_t delegation_state; struct rw_semaphore rwsem; #endif /* CONFIG_NFS_V4*/ diff --git a/include/linux/sunrpc/auth_gss.h b/include/linux/sunrpc/auth_gss.h index 671538d25bc1..8eee9dbbfe7a 100644 --- a/include/linux/sunrpc/auth_gss.h +++ b/include/linux/sunrpc/auth_gss.h @@ -69,7 +69,7 @@ struct gss_cl_ctx { enum rpc_gss_proc gc_proc; u32 gc_seq; spinlock_t gc_seq_lock; - struct gss_ctx *gc_gss_ctx; + struct gss_ctx __rcu *gc_gss_ctx; struct xdr_netobj gc_wire_ctx; u32 gc_win; unsigned long gc_expiry; @@ -80,7 +80,7 @@ struct gss_upcall_msg; struct gss_cred { struct rpc_cred gc_base; enum rpc_gss_svc gc_service; - struct gss_cl_ctx *gc_ctx; + struct gss_cl_ctx __rcu *gc_ctx; struct gss_upcall_msg *gc_upcall; unsigned long gc_upcall_timestamp; unsigned char gc_machine_cred : 1; From 2be85279281bafe7de808ca99de59af4fd474c49 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Thu, 4 Mar 2010 15:50:28 +0100 Subject: [PATCH 08/52] input: __rcu annotations Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Dmitry Torokhov Acked-by: Dmitry Torokhov Reviewed-by: Josh Triplett --- drivers/input/evdev.c | 2 +- include/linux/input.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c index c908c5f83645..5808731f72d2 100644 --- a/drivers/input/evdev.c +++ b/drivers/input/evdev.c @@ -28,7 +28,7 @@ struct evdev { int minor; struct input_handle handle; wait_queue_head_t wait; - struct evdev_client *grab; + struct evdev_client __rcu *grab; struct list_head client_list; spinlock_t client_lock; /* protects client_list */ struct mutex mutex; diff --git a/include/linux/input.h b/include/linux/input.h index 896a92227bc4..d6ae1761be97 100644 --- a/include/linux/input.h +++ b/include/linux/input.h @@ -1196,7 +1196,7 @@ struct input_dev { int (*flush)(struct input_dev *dev, struct file *file); int (*event)(struct input_dev *dev, unsigned int type, unsigned int code, int value); - struct input_handle *grab; + struct input_handle __rcu *grab; spinlock_t event_lock; struct mutex mutex; From 0906a372f2aa0fec1e59bd12b896883b6e41307a Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Tue, 9 Mar 2010 20:59:15 +0100 Subject: [PATCH 09/52] net/netfilter: __rcu annotations Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Acked-by: Patrick McHardy Cc: "David S. Miller" Cc: Eric Dumazet Reviewed-by: Josh Triplett --- include/net/netfilter/nf_conntrack.h | 2 +- net/ipv4/netfilter/nf_nat_core.c | 2 +- net/netfilter/core.c | 2 +- net/netfilter/nf_conntrack_ecache.c | 4 ++-- net/netfilter/nf_conntrack_extend.c | 2 +- net/netfilter/nf_conntrack_proto.c | 4 ++-- net/netfilter/nf_log.c | 2 +- net/netfilter/nf_queue.c | 2 +- 8 files changed, 10 insertions(+), 10 deletions(-) diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h index e624dae54fa4..caf17db87dbc 100644 --- a/include/net/netfilter/nf_conntrack.h +++ b/include/net/netfilter/nf_conntrack.h @@ -75,7 +75,7 @@ struct nf_conntrack_helper; /* nf_conn feature for connections that have a helper */ struct nf_conn_help { /* Helper. if any */ - struct nf_conntrack_helper *helper; + struct nf_conntrack_helper __rcu *helper; union nf_conntrack_help help; diff --git a/net/ipv4/netfilter/nf_nat_core.c b/net/ipv4/netfilter/nf_nat_core.c index 8c8632d9b93c..957c9241fb0c 100644 --- a/net/ipv4/netfilter/nf_nat_core.c +++ b/net/ipv4/netfilter/nf_nat_core.c @@ -38,7 +38,7 @@ static DEFINE_SPINLOCK(nf_nat_lock); static struct nf_conntrack_l3proto *l3proto __read_mostly; #define MAX_IP_NAT_PROTO 256 -static const struct nf_nat_protocol *nf_nat_protos[MAX_IP_NAT_PROTO] +static const struct nf_nat_protocol __rcu *nf_nat_protos[MAX_IP_NAT_PROTO] __read_mostly; static inline const struct nf_nat_protocol * diff --git a/net/netfilter/core.c b/net/netfilter/core.c index 78b505d33bfb..fdaec7daff1d 100644 --- a/net/netfilter/core.c +++ b/net/netfilter/core.c @@ -27,7 +27,7 @@ static DEFINE_MUTEX(afinfo_mutex); -const struct nf_afinfo *nf_afinfo[NFPROTO_NUMPROTO] __read_mostly; +const struct nf_afinfo __rcu *nf_afinfo[NFPROTO_NUMPROTO] __read_mostly; EXPORT_SYMBOL(nf_afinfo); int nf_register_afinfo(const struct nf_afinfo *afinfo) diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_ecache.c index cdcc7649476b..5702de35e2bb 100644 --- a/net/netfilter/nf_conntrack_ecache.c +++ b/net/netfilter/nf_conntrack_ecache.c @@ -26,10 +26,10 @@ static DEFINE_MUTEX(nf_ct_ecache_mutex); -struct nf_ct_event_notifier *nf_conntrack_event_cb __read_mostly; +struct nf_ct_event_notifier __rcu *nf_conntrack_event_cb __read_mostly; EXPORT_SYMBOL_GPL(nf_conntrack_event_cb); -struct nf_exp_event_notifier *nf_expect_event_cb __read_mostly; +struct nf_exp_event_notifier __rcu *nf_expect_event_cb __read_mostly; EXPORT_SYMBOL_GPL(nf_expect_event_cb); /* deliver cached events and clear cache entry - must be called with locally diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c index 7dcf7a404190..1d9bdae06161 100644 --- a/net/netfilter/nf_conntrack_extend.c +++ b/net/netfilter/nf_conntrack_extend.c @@ -16,7 +16,7 @@ #include #include -static struct nf_ct_ext_type *nf_ct_ext_types[NF_CT_EXT_NUM]; +static struct nf_ct_ext_type __rcu *nf_ct_ext_types[NF_CT_EXT_NUM]; static DEFINE_MUTEX(nf_ct_ext_type_mutex); void __nf_ct_ext_destroy(struct nf_conn *ct) diff --git a/net/netfilter/nf_conntrack_proto.c b/net/netfilter/nf_conntrack_proto.c index 5886ba1d52a0..ed6d92958023 100644 --- a/net/netfilter/nf_conntrack_proto.c +++ b/net/netfilter/nf_conntrack_proto.c @@ -28,8 +28,8 @@ #include #include -static struct nf_conntrack_l4proto **nf_ct_protos[PF_MAX] __read_mostly; -struct nf_conntrack_l3proto *nf_ct_l3protos[AF_MAX] __read_mostly; +static struct nf_conntrack_l4proto __rcu **nf_ct_protos[PF_MAX] __read_mostly; +struct nf_conntrack_l3proto __rcu *nf_ct_l3protos[AF_MAX] __read_mostly; EXPORT_SYMBOL_GPL(nf_ct_l3protos); static DEFINE_MUTEX(nf_ct_proto_mutex); diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c index 7df37fd786bc..b07393eab88e 100644 --- a/net/netfilter/nf_log.c +++ b/net/netfilter/nf_log.c @@ -16,7 +16,7 @@ #define NF_LOG_PREFIXLEN 128 #define NFLOGGER_NAME_LEN 64 -static const struct nf_logger *nf_loggers[NFPROTO_NUMPROTO] __read_mostly; +static const struct nf_logger __rcu *nf_loggers[NFPROTO_NUMPROTO] __read_mostly; static struct list_head nf_loggers_l[NFPROTO_NUMPROTO] __read_mostly; static DEFINE_MUTEX(nf_log_mutex); diff --git a/net/netfilter/nf_queue.c b/net/netfilter/nf_queue.c index 78b3cf9c519c..74aebed5bd28 100644 --- a/net/netfilter/nf_queue.c +++ b/net/netfilter/nf_queue.c @@ -18,7 +18,7 @@ * long term mutex. The handler must provide an an outfn() to accept packets * for queueing and must reinject all packets it receives, no matter what. */ -static const struct nf_queue_handler *queue_handler[NFPROTO_NUMPROTO] __read_mostly; +static const struct nf_queue_handler __rcu *queue_handler[NFPROTO_NUMPROTO] __read_mostly; static DEFINE_MUTEX(queue_handler_mutex); From 4b6a2872a2a00042ee50024822ab706e5456aad8 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Thu, 4 Mar 2010 15:59:23 +0100 Subject: [PATCH 10/52] kvm: add __rcu annotations Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Avi Kivity Cc: Marcelo Tosatti Reviewed-by: Josh Triplett --- include/linux/kvm_host.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index c13cc48697aa..ac740b26eb10 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -205,7 +205,7 @@ struct kvm { struct mutex irq_lock; #ifdef CONFIG_HAVE_KVM_IRQCHIP - struct kvm_irq_routing_table *irq_routing; + struct kvm_irq_routing_table __rcu *irq_routing; struct hlist_head mask_notifier_list; struct hlist_head irq_ack_notifier_list; #endif From 84483ea42cd4f2781d6e97a83ab3ebd0ff19fb10 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 16 Jun 2010 16:48:13 -0700 Subject: [PATCH 11/52] rcu: add shiny new debug assists to Documentation/RCU/checklist.txt Add a section describing PROVE_RCU, DEBUG_OBJECTS_RCU_HEAD, and the __rcu sparse checking to the RCU checklist. Suggested-by: David Miller Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- Documentation/RCU/checklist.txt | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index 790d1a812376..c7c6788956f4 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -365,3 +365,26 @@ over a rather long period of time, but improvements are always welcome! and the compiler to freely reorder code into and out of RCU read-side critical sections. It is the responsibility of the RCU update-side primitives to deal with this. + +17. Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and + the __rcu sparse checks to validate your RCU code. These + can help find problems as follows: + + CONFIG_PROVE_RCU: check that accesses to RCU-protected data + structures are carried out under the proper RCU + read-side critical section, while holding the right + combination of locks, or whatever other conditions + are appropriate. + + CONFIG_DEBUG_OBJECTS_RCU_HEAD: check that you don't pass the + same object to call_rcu() (or friends) before an RCU + grace period has elapsed since the last time that you + passed that same object to call_rcu() (or friends). + + __rcu sparse checks: tag the pointer to the RCU-protected data + structure with __rcu, and sparse will warn you if you + access that pointer without the services of one of the + variants of rcu_dereference(). + + These debugging aids can help you find problems that are + otherwise extremely difficult to spot. From e546f485e1d7520ca0200502cdcc11b503f4805c Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Mon, 21 Jun 2010 16:57:42 +0800 Subject: [PATCH 12/52] rcutorture: add random preemption Add random preemption to help we to torture the preemptable rcu. srcu_read_delay() also calls rcu_read_delay() for shorter delays. Added comment to preempt_schedule() call indicating that no quiescent states happen if preemption is disabled. Signed-off-by: Lai Jiangshan Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutorture.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 2e2726d790b9..729710273dcb 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -303,6 +303,10 @@ static void rcu_read_delay(struct rcu_random_state *rrsp) mdelay(longdelay_ms); if (!(rcu_random(rrsp) % (nrealreaders * 2 * shortdelay_us))) udelay(shortdelay_us); +#ifdef CONFIG_PREEMPT + if (!preempt_count() && !(rcu_random(rrsp) % (nrealreaders * 20000))) + preempt_schedule(); /* No QS if preempt_disable() in effect */ +#endif } static void rcu_torture_read_unlock(int idx) __releases(RCU) @@ -536,6 +540,8 @@ static void srcu_read_delay(struct rcu_random_state *rrsp) delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay * uspertick); if (!delay) schedule_timeout_interruptible(longdelay); + else + rcu_read_delay(rrsp); } static void srcu_torture_read_unlock(int idx) __releases(&srcu_ctl) From 394f99a9007d4274f7076bb8553ab0ff9707688b Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Mon, 28 Jun 2010 16:25:04 +0800 Subject: [PATCH 13/52] rcu: simplify the usage of percpu data &percpu_data is compatible with allocated percpu data. And we use it and remove the "->rda[NR_CPUS]" array, saving significant storage on systems with large numbers of CPUs. This does add an additional level of indirection and thus an additional cache line referenced, but because ->rda is not used on the read side, this is OK. Signed-off-by: Lai Jiangshan Reviewed-by: Tejun Heo Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 42 +++++++++++++++-------------------------- kernel/rcutree.h | 2 +- kernel/rcutree_plugin.h | 4 ++-- kernel/rcutree_trace.c | 2 +- 4 files changed, 19 insertions(+), 31 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index d5bc43976c5a..5b1c3c231bae 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -712,7 +712,7 @@ static void rcu_start_gp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { - struct rcu_data *rdp = rsp->rda[smp_processor_id()]; + struct rcu_data *rdp = this_cpu_ptr(rsp->rda); struct rcu_node *rnp = rcu_get_root(rsp); if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) { @@ -960,7 +960,7 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp) { int i; - struct rcu_data *rdp = rsp->rda[smp_processor_id()]; + struct rcu_data *rdp = this_cpu_ptr(rsp->rda); if (rdp->nxtlist == NULL) return; /* irqs disabled, so comparison is stable. */ @@ -984,7 +984,7 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) struct rcu_data *rdp; raw_spin_lock_irqsave(&rsp->onofflock, flags); - rdp = rsp->rda[smp_processor_id()]; + rdp = this_cpu_ptr(rsp->rda); if (rsp->orphan_cbs_list == NULL) { raw_spin_unlock_irqrestore(&rsp->onofflock, flags); return; @@ -1007,7 +1007,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) unsigned long flags; unsigned long mask; int need_report = 0; - struct rcu_data *rdp = rsp->rda[cpu]; + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp; /* Exclude any attempts to start a new grace period. */ @@ -1226,7 +1226,8 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) cpu = rnp->grplo; bit = 1; for (; cpu <= rnp->grphi; cpu++, bit <<= 1) { - if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu])) + if ((rnp->qsmask & bit) != 0 && + f(per_cpu_ptr(rsp->rda, cpu))) mask |= bit; } if (mask != 0) { @@ -1402,7 +1403,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), * a quiescent state betweentimes. */ local_irq_save(flags); - rdp = rsp->rda[smp_processor_id()]; + rdp = this_cpu_ptr(rsp->rda); rcu_process_gp_end(rsp, rdp); check_for_new_grace_period(rsp, rdp); @@ -1701,7 +1702,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) { unsigned long flags; int i; - struct rcu_data *rdp = rsp->rda[cpu]; + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rcu_get_root(rsp); /* Set up local state, ensuring consistent view of global state. */ @@ -1729,7 +1730,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable) { unsigned long flags; unsigned long mask; - struct rcu_data *rdp = rsp->rda[cpu]; + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rcu_get_root(rsp); /* Set up local state, ensuring consistent view of global state. */ @@ -1865,7 +1866,8 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp) /* * Helper function for rcu_init() that initializes one rcu_state structure. */ -static void __init rcu_init_one(struct rcu_state *rsp) +static void __init rcu_init_one(struct rcu_state *rsp, + struct rcu_data __percpu *rda) { static char *buf[] = { "rcu_node_level_0", "rcu_node_level_1", @@ -1918,37 +1920,23 @@ static void __init rcu_init_one(struct rcu_state *rsp) } } + rsp->rda = rda; rnp = rsp->level[NUM_RCU_LVLS - 1]; for_each_possible_cpu(i) { while (i > rnp->grphi) rnp++; - rsp->rda[i]->mynode = rnp; + per_cpu_ptr(rsp->rda, i)->mynode = rnp; rcu_boot_init_percpu_data(i, rsp); } } -/* - * Helper macro for __rcu_init() and __rcu_init_preempt(). To be used - * nowhere else! Assigns leaf node pointers into each CPU's rcu_data - * structure. - */ -#define RCU_INIT_FLAVOR(rsp, rcu_data) \ -do { \ - int i; \ - \ - for_each_possible_cpu(i) { \ - (rsp)->rda[i] = &per_cpu(rcu_data, i); \ - } \ - rcu_init_one(rsp); \ -} while (0) - void __init rcu_init(void) { int cpu; rcu_bootup_announce(); - RCU_INIT_FLAVOR(&rcu_sched_state, rcu_sched_data); - RCU_INIT_FLAVOR(&rcu_bh_state, rcu_bh_data); + rcu_init_one(&rcu_sched_state, &rcu_sched_data); + rcu_init_one(&rcu_bh_state, &rcu_bh_data); __rcu_init_preempt(); open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 14c040b18ed0..5ce197e87792 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -283,7 +283,7 @@ struct rcu_state { struct rcu_node *level[NUM_RCU_LVLS]; /* Hierarchy levels. */ u32 levelcnt[MAX_RCU_LVLS + 1]; /* # nodes in each level. */ u8 levelspread[NUM_RCU_LVLS]; /* kids/node in each level. */ - struct rcu_data *rda[NR_CPUS]; /* array of rdp pointers. */ + struct rcu_data __percpu *rda; /* pointer of percu rcu_data. */ /* The following fields are guarded by the root rcu_node's lock. */ diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 0e4f420245d9..9906f85c7780 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -154,7 +154,7 @@ static void rcu_preempt_note_context_switch(int cpu) (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { /* Possibly blocking in an RCU read-side critical section. */ - rdp = rcu_preempt_state.rda[cpu]; + rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); rnp = rdp->mynode; raw_spin_lock_irqsave(&rnp->lock, flags); t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; @@ -771,7 +771,7 @@ static void rcu_preempt_send_cbs_to_orphanage(void) */ static void __init __rcu_init_preempt(void) { - RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data); + rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); } /* diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index 36c95b45738e..458e032a3a30 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -262,7 +262,7 @@ static void print_rcu_pendings(struct seq_file *m, struct rcu_state *rsp) struct rcu_data *rdp; for_each_possible_cpu(cpu) { - rdp = rsp->rda[cpu]; + rdp = per_cpu_ptr(rsp->rda, cpu); if (rdp->beenonline) print_one_rcu_pending(m, rdp); } From 4221a9918e38b7494cee341dda7b7b4bb8c04bde Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Sat, 26 Jun 2010 01:08:19 +0900 Subject: [PATCH 14/52] Add RCU check for find_task_by_vpid(). find_task_by_vpid() says "Must be called under rcu_read_lock().". But due to commit 3120438 "rcu: Disable lockdep checking in RCU list-traversal primitives", we are currently unable to catch "find_task_by_vpid() with tasklist_lock held but RCU lock not held" errors due to the RCU-lockdep checks being suppressed in the RCU variants of the struct list_head traversals. This commit therefore places an explicit check for being in an RCU read-side critical section in find_task_by_pid_ns(). =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- kernel/pid.c:386 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 1 lock held by rc.sysinit/1102: #0: (tasklist_lock){.+.+..}, at: [] sys_setpgid+0x40/0x160 stack backtrace: Pid: 1102, comm: rc.sysinit Not tainted 2.6.35-rc3-dirty #1 Call Trace: [] lockdep_rcu_dereference+0x94/0xb0 [] find_task_by_pid_ns+0x6d/0x70 [] find_task_by_vpid+0x18/0x20 [] sys_setpgid+0x47/0x160 [] sysenter_do_call+0x12/0x36 Commit updated to use a new rcu_lockdep_assert() exported API rather than the old internal __do_rcu_dereference(). Signed-off-by: Tetsuo Handa Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 14 +++++++++----- kernel/pid.c | 1 + 2 files changed, 10 insertions(+), 5 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index b973dea2d6b0..b124bc6a75ad 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -215,7 +215,11 @@ static inline int rcu_read_lock_sched_held(void) extern int rcu_my_thread_group_empty(void); -#define __do_rcu_dereference_check(c) \ +/** + * rcu_lockdep_assert - emit lockdep splat if specified condition not met + * @c: condition to check + */ +#define rcu_lockdep_assert(c) \ do { \ static bool __warned; \ if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ @@ -226,7 +230,7 @@ extern int rcu_my_thread_group_empty(void); #else /* #ifdef CONFIG_PROVE_RCU */ -#define __do_rcu_dereference_check(c) do { } while (0) +#define rcu_lockdep_assert(c) do { } while (0) #endif /* #else #ifdef CONFIG_PROVE_RCU */ @@ -247,14 +251,14 @@ extern int rcu_my_thread_group_empty(void); #define __rcu_dereference_check(p, c, space) \ ({ \ typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ - __do_rcu_dereference_check(c); \ + rcu_lockdep_assert(c); \ (void) (((typeof (*p) space *)p) == p); \ smp_read_barrier_depends(); \ ((typeof(*p) __force __kernel *)(_________p1)); \ }) #define __rcu_dereference_protected(p, c, space) \ ({ \ - __do_rcu_dereference_check(c); \ + rcu_lockdep_assert(c); \ (void) (((typeof (*p) space *)p) == p); \ ((typeof(*p) __force __kernel *)(p)); \ }) @@ -262,7 +266,7 @@ extern int rcu_my_thread_group_empty(void); #define __rcu_dereference_index_check(p, c) \ ({ \ typeof(p) _________p1 = ACCESS_ONCE(p); \ - __do_rcu_dereference_check(c); \ + rcu_lockdep_assert(c); \ smp_read_barrier_depends(); \ (_________p1); \ }) diff --git a/kernel/pid.c b/kernel/pid.c index 0f90c2f713f1..39b65b69584f 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -416,6 +416,7 @@ EXPORT_SYMBOL(pid_task); */ struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns) { + rcu_lockdep_assert(rcu_read_lock_held()); return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID); } From b163760e37047781b37c412cde54d146ac4b651f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 2 Jun 2010 16:21:38 -0700 Subject: [PATCH 15/52] rcu: make CPU stall warning timeout configurable Also set the default to 60 seconds, up from the previous hard-coded timeout of 10 seconds. This allows people who care to set short timeouts, while avoiding people with unusual configurations (make randconfig!!!) from being bothered with spurious CPU stall warnings. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.h | 5 +++-- lib/Kconfig.debug | 11 +++++++++++ 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 5ce197e87792..183ebf405315 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -254,9 +254,10 @@ struct rcu_data { #define RCU_STALL_DELAY_DELTA 0 #endif -#define RCU_SECONDS_TILL_STALL_CHECK (10 * HZ + RCU_STALL_DELAY_DELTA) +#define RCU_SECONDS_TILL_STALL_CHECK (CONFIG_RCU_CPU_STALL_TIMEOUT * HZ + \ + RCU_STALL_DELAY_DELTA) /* for rsp->jiffies_stall */ -#define RCU_SECONDS_TILL_STALL_RECHECK (30 * HZ + RCU_STALL_DELAY_DELTA) +#define RCU_SECONDS_TILL_STALL_RECHECK (3 * RCU_SECONDS_TILL_STALL_CHECK + 30) /* for rsp->jiffies_stall */ #define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */ /* to take at least one */ diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 12465f2ef766..b5005b762103 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -845,6 +845,17 @@ config RCU_CPU_STALL_DETECTOR Say Y if you are unsure. +config RCU_CPU_STALL_TIMEOUT + int "RCU CPU stall timeout in seconds" + depends on RCU_CPU_STALL_DETECTOR + range 3 300 + default 60 + help + If a given RCU grace period extends more than the specified + number of seconds, a CPU stall warning is printed. If the + RCU grace period persists, additional CPU stall warnings are + printed at more widely spaced intervals. + config RCU_CPU_STALL_VERBOSE bool "Print additional per-task information for RCU_CPU_STALL_DETECTOR" depends on RCU_CPU_STALL_DETECTOR && TREE_PREEMPT_RCU From 742734eea0cf5314cde5945963ed964be167bd84 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 30 Jun 2010 11:43:52 -0700 Subject: [PATCH 16/52] rcu: add boot parameter to suppress RCU CPU stall warning messages Although the RCU CPU stall warning messages are a very good way to alert people to a problem, once alerted, it is sometimes helpful to shut them off in order to avoid obscuring other messages that might be being used to track down the problem. Although you can rebuild the kernel with CONFIG_RCU_CPU_STALL_DETECTOR=n, this is sometimes inconvenient. This commit therefore adds a boot parameter named "rcu_cpu_stall_suppress" that shuts these messages off without requiring a rebuild (though a reboot might be needed for those not brave enough to patch their kernel while it is running). This message-suppression was already in place for the panic case, so this commit need only rename the variable and export it via module_param(). Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 5b1c3c231bae..f3d5906cbc21 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -143,6 +143,11 @@ module_param(blimit, int, 0); module_param(qhimark, int, 0); module_param(qlowmark, int, 0); +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR +int rcu_cpu_stall_suppress __read_mostly; +module_param(rcu_cpu_stall_suppress, int, 0); +#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ + static void force_quiescent_state(struct rcu_state *rsp, int relaxed); static int rcu_pending(int cpu); @@ -450,7 +455,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) #ifdef CONFIG_RCU_CPU_STALL_DETECTOR -int rcu_cpu_stall_panicking __read_mostly; +int rcu_cpu_stall_suppress __read_mostly; static void record_gp_stall_check_time(struct rcu_state *rsp) { @@ -530,7 +535,7 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) long delta; struct rcu_node *rnp; - if (rcu_cpu_stall_panicking) + if (rcu_cpu_stall_suppress) return; delta = jiffies - rsp->jiffies_stall; rnp = rdp->mynode; @@ -548,7 +553,7 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) { - rcu_cpu_stall_panicking = 1; + rcu_cpu_stall_suppress = 1; return NOTIFY_DONE; } From 77d8485a8b5416c615b6acd95f01bfcacd7d81ff Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 8 Jul 2010 17:38:59 -0700 Subject: [PATCH 17/52] rcu: improve kerneldoc for rcu_read_lock(), call_rcu(), and synchronize_rcu() Make it explicit that new RCU read-side critical sections that start after call_rcu() and synchronize_rcu() start might still be running after the end of the relevant grace period. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 16 +++++++++------- kernel/rcutree_plugin.h | 8 +++++--- 2 files changed, 14 insertions(+), 10 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index b124bc6a75ad..3e1b6625553b 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -450,7 +450,7 @@ extern int rcu_my_thread_group_empty(void); * until after the all the other CPUs exit their critical sections. * * Note, however, that RCU callbacks are permitted to run concurrently - * with RCU read-side critical sections. One way that this can happen + * with new RCU read-side critical sections. One way that this can happen * is via the following sequence of events: (1) CPU 0 enters an RCU * read-side critical section, (2) CPU 1 invokes call_rcu() to register * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, @@ -608,11 +608,13 @@ extern void wakeme_after_rcu(struct rcu_head *head); /** * call_rcu() - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. - * @func: actual update function to be invoked after the grace period + * @func: actual callback function to be invoked after the grace period * - * The update function will be invoked some time after a full grace - * period elapses, in other words after all currently executing RCU - * read-side critical sections have completed. RCU read-side critical + * The callback function will be invoked some time after a full grace + * period elapses, in other words after all pre-existing RCU read-side + * critical sections have completed. However, the callback function + * might well execute concurrently with RCU read-side critical sections + * that started after call_rcu() was invoked. RCU read-side critical * sections are delimited by rcu_read_lock() and rcu_read_unlock(), * and may be nested. */ @@ -622,9 +624,9 @@ extern void call_rcu(struct rcu_head *head, /** * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. * @head: structure to be used for queueing the RCU updates. - * @func: actual update function to be invoked after the grace period + * @func: actual callback function to be invoked after the grace period * - * The update function will be invoked some time after a full grace + * The callback function will be invoked some time after a full grace * period elapses, in other words after all currently executing RCU * read-side critical sections have completed. call_rcu_bh() assumes * that the read-side critical sections end on completion of a softirq diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 9906f85c7780..63bb7714fdeb 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -546,9 +546,11 @@ EXPORT_SYMBOL_GPL(call_rcu); * * Control will return to the caller some time after a full grace * period has elapsed, in other words after all currently executing RCU - * read-side critical sections have completed. RCU read-side critical - * sections are delimited by rcu_read_lock() and rcu_read_unlock(), - * and may be nested. + * read-side critical sections have completed. Note, however, that + * upon return from synchronize_rcu(), the caller might well be executing + * concurrently with new RCU read-side critical sections that began while + * synchronize_rcu() was waiting. RCU read-side critical sections are + * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. */ void synchronize_rcu(void) { From 374a8e0dc33c984fac284de7d57d77af3cfdbfb7 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Wed, 24 Feb 2010 20:00:13 +0100 Subject: [PATCH 18/52] notifiers: __rcu annotations Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Alan Cox Reviewed-by: Josh Triplett --- include/linux/notifier.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/include/linux/notifier.h b/include/linux/notifier.h index b2f1a4d83550..2026f9e1ceb8 100644 --- a/include/linux/notifier.h +++ b/include/linux/notifier.h @@ -49,28 +49,28 @@ struct notifier_block { int (*notifier_call)(struct notifier_block *, unsigned long, void *); - struct notifier_block *next; + struct notifier_block __rcu *next; int priority; }; struct atomic_notifier_head { spinlock_t lock; - struct notifier_block *head; + struct notifier_block __rcu *head; }; struct blocking_notifier_head { struct rw_semaphore rwsem; - struct notifier_block *head; + struct notifier_block __rcu *head; }; struct raw_notifier_head { - struct notifier_block *head; + struct notifier_block __rcu *head; }; struct srcu_notifier_head { struct mutex mutex; struct srcu_struct srcu; - struct notifier_block *head; + struct notifier_block __rcu *head; }; #define ATOMIC_INIT_NOTIFIER_HEAD(name) do { \ From a1115570b31091f3e3ab9e6cf7ee8d320a42be84 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Thu, 25 Feb 2010 23:43:52 +0100 Subject: [PATCH 19/52] radix-tree: __rcu annotations Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Nick Piggin Reviewed-by: Josh Triplett --- include/linux/radix-tree.h | 4 +++- lib/radix-tree.c | 2 +- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h index 634b8e674ac5..a39cbed9ee17 100644 --- a/include/linux/radix-tree.h +++ b/include/linux/radix-tree.h @@ -47,6 +47,8 @@ static inline void *radix_tree_indirect_to_ptr(void *ptr) { return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR); } +#define radix_tree_indirect_to_ptr(ptr) \ + radix_tree_indirect_to_ptr((void __force *)(ptr)) static inline int radix_tree_is_indirect_ptr(void *ptr) { @@ -61,7 +63,7 @@ static inline int radix_tree_is_indirect_ptr(void *ptr) struct radix_tree_root { unsigned int height; gfp_t gfp_mask; - struct radix_tree_node *rnode; + struct radix_tree_node __rcu *rnode; }; #define RADIX_TREE_INIT(mask) { \ diff --git a/lib/radix-tree.c b/lib/radix-tree.c index e907858498a6..899fb750946f 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -49,7 +49,7 @@ struct radix_tree_node { unsigned int height; /* Height from the bottom */ unsigned int count; struct rcu_head rcu_head; - void *slots[RADIX_TREE_MAP_SIZE]; + void __rcu *slots[RADIX_TREE_MAP_SIZE]; unsigned long tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS]; }; From d2c2486bc8e185548490e8edbc84d185de9eaff1 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Fri, 26 Feb 2010 14:53:26 +0100 Subject: [PATCH 20/52] idr: __rcu annotations Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Manfred Spraul Reviewed-by: Josh Triplett --- include/linux/idr.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/idr.h b/include/linux/idr.h index e968db71e33a..cdb715e58e3e 100644 --- a/include/linux/idr.h +++ b/include/linux/idr.h @@ -50,14 +50,14 @@ struct idr_layer { unsigned long bitmap; /* A zero bit means "space here" */ - struct idr_layer *ary[1< Date: Wed, 24 Feb 2010 20:01:56 +0100 Subject: [PATCH 21/52] kernel: __rcu annotations This adds annotations for RCU operations in core kernel components Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Al Viro Cc: Jens Axboe Cc: Andrew Morton Reviewed-by: Josh Triplett --- include/linux/fdtable.h | 6 +++--- include/linux/fs.h | 2 +- include/linux/genhd.h | 6 +++--- include/linux/init_task.h | 4 ++-- include/linux/iocontext.h | 2 +- include/linux/mm_types.h | 2 +- 6 files changed, 11 insertions(+), 11 deletions(-) diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h index f59ed297b661..133c0ba25e30 100644 --- a/include/linux/fdtable.h +++ b/include/linux/fdtable.h @@ -31,7 +31,7 @@ struct embedded_fd_set { struct fdtable { unsigned int max_fds; - struct file ** fd; /* current fd array */ + struct file __rcu **fd; /* current fd array */ fd_set *close_on_exec; fd_set *open_fds; struct rcu_head rcu; @@ -46,7 +46,7 @@ struct files_struct { * read mostly part */ atomic_t count; - struct fdtable *fdt; + struct fdtable __rcu *fdt; struct fdtable fdtab; /* * written part on a separate cache line in SMP @@ -55,7 +55,7 @@ struct files_struct { int next_fd; struct embedded_fd_set close_on_exec_init; struct embedded_fd_set open_fds_init; - struct file * fd_array[NR_OPEN_DEFAULT]; + struct file __rcu * fd_array[NR_OPEN_DEFAULT]; }; #define rcu_dereference_check_fdtable(files, fdtfd) \ diff --git a/include/linux/fs.h b/include/linux/fs.h index 76041b614758..aa3dc8d20436 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1380,7 +1380,7 @@ struct super_block { * Saved mount options for lazy filesystems using * generic_show_options() */ - char *s_options; + char __rcu *s_options; }; extern struct timespec current_fs_time(struct super_block *sb); diff --git a/include/linux/genhd.h b/include/linux/genhd.h index 5f2f4c4d8fb0..af3f06b41dc1 100644 --- a/include/linux/genhd.h +++ b/include/linux/genhd.h @@ -129,8 +129,8 @@ struct blk_scsi_cmd_filter { struct disk_part_tbl { struct rcu_head rcu_head; int len; - struct hd_struct *last_lookup; - struct hd_struct *part[]; + struct hd_struct __rcu *last_lookup; + struct hd_struct __rcu *part[]; }; struct gendisk { @@ -149,7 +149,7 @@ struct gendisk { * non-critical accesses use RCU. Always access through * helpers. */ - struct disk_part_tbl *part_tbl; + struct disk_part_tbl __rcu *part_tbl; struct hd_struct part0; const struct block_device_operations *fops; diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 1f43fa56f600..6460fc65ed6b 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -137,8 +137,8 @@ extern struct cred init_cred; .children = LIST_HEAD_INIT(tsk.children), \ .sibling = LIST_HEAD_INIT(tsk.sibling), \ .group_leader = &tsk, \ - .real_cred = &init_cred, \ - .cred = &init_cred, \ + RCU_INIT_POINTER(.real_cred, &init_cred), \ + RCU_INIT_POINTER(.cred, &init_cred), \ .cred_guard_mutex = \ __MUTEX_INITIALIZER(tsk.cred_guard_mutex), \ .comm = "swapper", \ diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h index 64d529133031..3e70b21884a9 100644 --- a/include/linux/iocontext.h +++ b/include/linux/iocontext.h @@ -53,7 +53,7 @@ struct io_context { struct radix_tree_root radix_root; struct hlist_head cic_list; - void *ioc_data; + void __rcu *ioc_data; }; static inline struct io_context *ioc_task_link(struct io_context *ioc) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index b8bb9a6a1f37..05537a5eb855 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -299,7 +299,7 @@ struct mm_struct { * new_owner->mm == mm * new_owner->alloc_lock is held */ - struct task_struct *owner; + struct task_struct __rcu *owner; #endif #ifdef CONFIG_PROC_FS From 5e8067adfdbaf97039a97540765b1e16eb8d61cc Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Sat, 17 Apr 2010 08:48:41 -0400 Subject: [PATCH 22/52] rcu head remove init RCU heads really don't need to be initialized. Their state before call_rcu() really does not matter. We need to keep init/destroy_rcu_head_on_stack() though, since we want debugobjects to be able to keep track of these objects. Signed-off-by: Alexey Dobriyan Signed-off-by: Mathieu Desnoyers CC: David S. Miller CC: "Paul E. McKenney" CC: akpm@linux-foundation.org CC: mingo@elte.hu CC: laijs@cn.fujitsu.com CC: dipankar@in.ibm.com CC: josh@joshtriplett.org CC: dvhltc@us.ibm.com CC: niv@us.ibm.com CC: tglx@linutronix.de CC: peterz@infradead.org CC: rostedt@goodmis.org CC: Valdis.Kletnieks@vt.edu CC: dhowells@redhat.com CC: eric.dumazet@gmail.com CC: Alexey Dobriyan Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 6 ------ 1 file changed, 6 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 3e1b6625553b..27b44b3e3024 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -75,12 +75,6 @@ extern void rcu_init(void); #error "Unknown RCU implementation specified to kernel configuration" #endif -#define RCU_HEAD_INIT { .next = NULL, .func = NULL } -#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT -#define INIT_RCU_HEAD(ptr) do { \ - (ptr)->next = NULL; (ptr)->func = NULL; \ -} while (0) - /* * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic * initialization and destruction of rcu_head on the stack. rcu_head structures From 65e423f8ee5843e1ea3f2d94adf4ba3560a17f7b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 19 May 2010 10:42:16 -0700 Subject: [PATCH 23/52] Update documentation to note the passage of INIT_RCU_HEAD() Signed-off-by: Alexey Dobriyan Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- Documentation/DocBook/kernel-locking.tmpl | 8 -------- 1 file changed, 8 deletions(-) diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl index 084f6ad7b7a0..e6cc57460212 100644 --- a/Documentation/DocBook/kernel-locking.tmpl +++ b/Documentation/DocBook/kernel-locking.tmpl @@ -1725,14 +1725,6 @@ the amount of locking which needs to be done. if (++cache_num > MAX_CACHE_SIZE) { struct object *i, *outcast = NULL; list_for_each_entry(i, &cache, list) { -@@ -85,6 +94,7 @@ - obj->popularity = 0; - atomic_set(&obj->refcnt, 1); /* The cache holds a reference */ - spin_lock_init(&obj->lock); -+ INIT_RCU_HEAD(&obj->rcu); - - spin_lock_irqsave(&cache_lock, flags); - __cache_add(obj); @@ -104,12 +114,11 @@ struct object *cache_find(int id) { From ded5e5ed2f3348ba2f9a319c6497e46c22850e97 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 19 May 2010 10:46:55 -0700 Subject: [PATCH 24/52] Update call_rcu() usage, add synchronize_rcu() Reported-by: Kyle Hubert Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- Documentation/DocBook/kernel-locking.tmpl | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl index e6cc57460212..ed64d220baf2 100644 --- a/Documentation/DocBook/kernel-locking.tmpl +++ b/Documentation/DocBook/kernel-locking.tmpl @@ -1645,7 +1645,9 @@ the amount of locking which needs to be done. all the readers who were traversing the list when we deleted the element are finished. We use call_rcu() to register a callback which will actually destroy the object once - the readers are finished. + all pre-existing readers are finished. Alternatively, + synchronize_rcu() may be used to block until + all pre-existing are finished. But how does Read Copy Update know when the readers are @@ -1714,7 +1716,7 @@ the amount of locking which needs to be done. - object_put(obj); + list_del_rcu(&obj->list); cache_num--; -+ call_rcu(&obj->rcu, cache_delete_rcu, obj); ++ call_rcu(&obj->rcu, cache_delete_rcu); } /* Must be holding cache_lock */ From f2e0dd7090eddef427ab9d9f81de122244cded51 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 14 Jul 2010 14:38:30 -0700 Subject: [PATCH 25/52] rcu: allow RCU CPU stall warning messages to be controlled in /sys Set the permissions of the rcu_cpu_stall_suppress to 644 to enable RCU CPU stall warnings to be enabled and disabled at runtime via sysfs. Suggested-by: Josh Triplett Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f3d5906cbc21..5d910beefff2 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -145,7 +145,7 @@ module_param(qlowmark, int, 0); #ifdef CONFIG_RCU_CPU_STALL_DETECTOR int rcu_cpu_stall_suppress __read_mostly; -module_param(rcu_cpu_stall_suppress, int, 0); +module_param(rcu_cpu_stall_suppress, int, 0644); #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ static void force_quiescent_state(struct rcu_state *rsp, int relaxed); From 687d7a960aea46e016182c7ce346d62c4dbd0366 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 21 Jul 2010 06:52:40 -0700 Subject: [PATCH 26/52] rcu: restrict TREE_RCU to SMP builds with !PREEMPT Because both TINY_RCU and TREE_PREEMPT_RCU have been in mainline for several releases, it is time to restrict the use of TREE_RCU to SMP non-preemptible systems. This reduces testing/validation effort. This commit is a first step towards driving the selection of RCU implementation directly off of the SMP and PREEMPT configuration parameters. Signed-off-by: Paul E. McKenney --- init/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/init/Kconfig b/init/Kconfig index 2de5b1cbadd9..79ac52bef4ce 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -340,6 +340,7 @@ choice config TREE_RCU bool "Tree-based hierarchical RCU" + depends on !PREEMPT && SMP help This option selects the RCU implementation that is designed for very large SMP system with hundreds or From 910b1b7e19a292ff685001caf1bf1a9775b771a1 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 21 Jul 2010 08:05:56 -0700 Subject: [PATCH 27/52] rcu: Allow RCU CPU stall warnings to be off at boot, but manually enablable Currently, if RCU CPU stall warnings are enabled, they are enabled immediately upon boot. They can be manually disabled via /sys (and also re-enabled via /sys), and are automatically disabled upon panic. However, some users need RCU CPU stalls to be disabled at boot time, but to be enabled without rebuilding/rebooting. For example, someone running a real-time application in production might not want the additional latency of RCU CPU stall detection in normal operation, but might need to enable it at any point for fault isolation purposes. This commit therefore provides a new CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE kernel configuration parameter that maintains the current behavior (enable at boot) by default, but allows a kernel to be configured with RCU CPU stall detection built into the kernel, but disabled at boot time. Requested-by: Clark Williams Requested-by: John Kacur Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 2 +- kernel/rcutree.h | 6 ++++++ lib/Kconfig.debug | 13 +++++++++++++ 3 files changed, 20 insertions(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 5d910beefff2..5aab7dabd0d5 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -144,7 +144,7 @@ module_param(qhimark, int, 0); module_param(qlowmark, int, 0); #ifdef CONFIG_RCU_CPU_STALL_DETECTOR -int rcu_cpu_stall_suppress __read_mostly; +int rcu_cpu_stall_suppress __read_mostly = RCU_CPU_STALL_SUPPRESS_INIT; module_param(rcu_cpu_stall_suppress, int, 0644); #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 183ebf405315..bb4d08695c45 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -264,6 +264,12 @@ struct rcu_data { /* scheduling clock irq */ /* before ratting on them. */ +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE +#define RCU_CPU_STALL_SUPPRESS_INIT 0 +#else +#define RCU_CPU_STALL_SUPPRESS_INIT 1 +#endif + #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index b5005b762103..52c2172dff16 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -856,6 +856,19 @@ config RCU_CPU_STALL_TIMEOUT RCU grace period persists, additional CPU stall warnings are printed at more widely spaced intervals. +config RCU_CPU_STALL_DETECTOR_RUNNABLE + bool "RCU CPU stall checking starts automatically at boot" + depends on RCU_CPU_STALL_DETECTOR + default y + help + If set, start checking for RCU CPU stalls immediately on + boot. Otherwise, RCU CPU stall checking must be manually + enabled. + + Say Y if you are unsure. + + Say N if you wish to suppress RCU CPU stall checking during boot. + config RCU_CPU_STALL_VERBOSE bool "Print additional per-task information for RCU_CPU_STALL_DETECTOR" depends on RCU_CPU_STALL_DETECTOR && TREE_PREEMPT_RCU From 4d87ffadbba88105f33271bef5f2c79366c6a4e1 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 4 Aug 2010 17:31:12 -0700 Subject: [PATCH 28/52] rcu: Fix RCU_FANOUT help message Commit cf244dc01bf68 added a fourth level to the TREE_RCU hierarchy, but the RCU_FANOUT help message still said "cube root". This commit fixes this to "fourth root" and also emphasizes that production systems are well-served by the default. (Stress-testing RCU itself uses small RCU_FANOUT values in order to test large-system code paths on small(er) systems.) Located-by: John Kacur Signed-off-by: Paul E. McKenney --- init/Kconfig | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 79ac52bef4ce..dbc08baad77e 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -388,9 +388,12 @@ config RCU_FANOUT help This option controls the fanout of hierarchical implementations of RCU, allowing RCU to work efficiently on machines with - large numbers of CPUs. This value must be at least the cube - root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit - systems and up to 262,144 for 64-bit systems. + large numbers of CPUs. This value must be at least the fourth + root of NR_CPUS, which allows NR_CPUS to be insanely large. + The default value of RCU_FANOUT should be used for production + systems, but if you are stress-testing the RCU implementation + itself, small RCU_FANOUT values allow you to test large-system + code paths on small(er) systems. Select a specific number if testing RCU itself. Take the default if unsure. From a57eb940d130477a799dfb24a570ee04979c0f7f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 29 Jun 2010 16:49:16 -0700 Subject: [PATCH 29/52] rcu: Add a TINY_PREEMPT_RCU MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier Signed-off-by: Paul E. McKenney --- include/linux/hardirq.h | 2 +- include/linux/init_task.h | 10 +- include/linux/rcupdate.h | 3 +- include/linux/rcutiny.h | 164 +++++++---- include/linux/rcutree.h | 2 + include/linux/sched.h | 10 +- init/Kconfig | 16 +- kernel/Makefile | 1 + kernel/rcutiny.c | 33 +-- kernel/rcutiny_plugin.h | 582 +++++++++++++++++++++++++++++++++++++- 10 files changed, 736 insertions(+), 87 deletions(-) diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index d5b387669dab..1f4517d55b19 100644 --- a/include/linux/hardirq.h +++ b/include/linux/hardirq.h @@ -139,7 +139,7 @@ static inline void account_system_vtime(struct task_struct *tsk) #endif #if defined(CONFIG_NO_HZ) -#if defined(CONFIG_TINY_RCU) +#if defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) extern void rcu_enter_nohz(void); extern void rcu_exit_nohz(void); diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 6460fc65ed6b..2fea6c8ef6ba 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -82,11 +82,17 @@ extern struct group_info init_groups; # define CAP_INIT_BSET CAP_FULL_SET #ifdef CONFIG_TREE_PREEMPT_RCU +#define INIT_TASK_RCU_TREE_PREEMPT() \ + .rcu_blocked_node = NULL, +#else +#define INIT_TASK_RCU_TREE_PREEMPT(tsk) +#endif +#ifdef CONFIG_PREEMPT_RCU #define INIT_TASK_RCU_PREEMPT(tsk) \ .rcu_read_lock_nesting = 0, \ .rcu_read_unlock_special = 0, \ - .rcu_blocked_node = NULL, \ - .rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry), + .rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry), \ + INIT_TASK_RCU_TREE_PREEMPT() #else #define INIT_TASK_RCU_PREEMPT(tsk) #endif diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 27b44b3e3024..24b896649384 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -58,7 +58,6 @@ struct rcu_head { }; /* Exported common interfaces */ -extern void rcu_barrier(void); extern void rcu_barrier_bh(void); extern void rcu_barrier_sched(void); extern void synchronize_sched_expedited(void); @@ -69,7 +68,7 @@ extern void rcu_init(void); #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) #include -#elif defined(CONFIG_TINY_RCU) +#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) #include #else #error "Unknown RCU implementation specified to kernel configuration" diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index e2e893144a84..4cc5eba41616 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -29,25 +29,127 @@ void rcu_sched_qs(int cpu); void rcu_bh_qs(int cpu); -static inline void rcu_note_context_switch(int cpu) -{ - rcu_sched_qs(cpu); -} +#ifdef CONFIG_TINY_RCU #define __rcu_read_lock() preempt_disable() #define __rcu_read_unlock() preempt_enable() +#else /* #ifdef CONFIG_TINY_RCU */ +void __rcu_read_lock(void); +void __rcu_read_unlock(void); +#endif /* #else #ifdef CONFIG_TINY_RCU */ #define __rcu_read_lock_bh() local_bh_disable() #define __rcu_read_unlock_bh() local_bh_enable() -#define call_rcu_sched call_rcu +extern void call_rcu_sched(struct rcu_head *head, + void (*func)(struct rcu_head *rcu)); #define rcu_init_sched() do { } while (0) -extern void rcu_check_callbacks(int cpu, int user); + +extern void synchronize_sched(void); + +#ifdef CONFIG_TINY_RCU + +#define call_rcu call_rcu_sched + +static inline void synchronize_rcu(void) +{ + synchronize_sched(); +} + +static inline void synchronize_rcu_expedited(void) +{ + synchronize_sched(); /* Only one CPU, so pretty fast anyway!!! */ +} + +static inline void rcu_barrier(void) +{ + rcu_barrier_sched(); /* Only one CPU, so only one list of callbacks! */ +} + +#else /* #ifdef CONFIG_TINY_RCU */ + +void synchronize_rcu(void); +void rcu_barrier(void); +void synchronize_rcu_expedited(void); + +#endif /* #else #ifdef CONFIG_TINY_RCU */ + +static inline void synchronize_rcu_bh(void) +{ + synchronize_sched(); +} + +static inline void synchronize_rcu_bh_expedited(void) +{ + synchronize_sched(); +} + +struct notifier_block; + +#ifdef CONFIG_NO_HZ + +extern void rcu_enter_nohz(void); +extern void rcu_exit_nohz(void); + +#else /* #ifdef CONFIG_NO_HZ */ + +static inline void rcu_enter_nohz(void) +{ +} + +static inline void rcu_exit_nohz(void) +{ +} + +#endif /* #else #ifdef CONFIG_NO_HZ */ + +#ifdef CONFIG_TINY_RCU + +static inline void rcu_preempt_note_context_switch(void) +{ +} + +static inline void exit_rcu(void) +{ +} static inline int rcu_needs_cpu(int cpu) { return 0; } +static inline int rcu_preempt_depth(void) +{ + return 0; +} + +#else /* #ifdef CONFIG_TINY_RCU */ + +void rcu_preempt_note_context_switch(void); +extern void exit_rcu(void); +int rcu_preempt_needs_cpu(void); + +static inline int rcu_needs_cpu(int cpu) +{ + return rcu_preempt_needs_cpu(); +} + +/* + * Defined as macro as it is a very low level header + * included from areas that don't even know about current + * FIXME: combine with include/linux/rcutree.h into rcupdate.h. + */ +#define rcu_preempt_depth() (current->rcu_read_lock_nesting) + +#endif /* #else #ifdef CONFIG_TINY_RCU */ + +static inline void rcu_note_context_switch(int cpu) +{ + rcu_sched_qs(cpu); + rcu_preempt_note_context_switch(); +} + +extern void rcu_check_callbacks(int cpu, int user); + /* * Return the number of grace periods. */ @@ -76,56 +178,6 @@ static inline void rcu_sched_force_quiescent_state(void) { } -extern void synchronize_sched(void); - -static inline void synchronize_rcu(void) -{ - synchronize_sched(); -} - -static inline void synchronize_rcu_bh(void) -{ - synchronize_sched(); -} - -static inline void synchronize_rcu_expedited(void) -{ - synchronize_sched(); -} - -static inline void synchronize_rcu_bh_expedited(void) -{ - synchronize_sched(); -} - -struct notifier_block; - -#ifdef CONFIG_NO_HZ - -extern void rcu_enter_nohz(void); -extern void rcu_exit_nohz(void); - -#else /* #ifdef CONFIG_NO_HZ */ - -static inline void rcu_enter_nohz(void) -{ -} - -static inline void rcu_exit_nohz(void) -{ -} - -#endif /* #else #ifdef CONFIG_NO_HZ */ - -static inline void exit_rcu(void) -{ -} - -static inline int rcu_preempt_depth(void) -{ - return 0; -} - #ifdef CONFIG_DEBUG_LOCK_ALLOC extern int rcu_scheduler_active __read_mostly; diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index c0ed1c056f29..c13b85dd22bc 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -95,6 +95,8 @@ static inline void synchronize_rcu_bh_expedited(void) synchronize_sched_expedited(); } +extern void rcu_barrier(void); + extern void rcu_check_callbacks(int cpu, int user); extern long rcu_batches_completed(void); diff --git a/include/linux/sched.h b/include/linux/sched.h index 2c756666c111..e18473f0eb78 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1202,11 +1202,13 @@ struct task_struct { unsigned int policy; cpumask_t cpus_allowed; -#ifdef CONFIG_TREE_PREEMPT_RCU +#ifdef CONFIG_PREEMPT_RCU int rcu_read_lock_nesting; char rcu_read_unlock_special; - struct rcu_node *rcu_blocked_node; struct list_head rcu_node_entry; +#endif /* #ifdef CONFIG_PREEMPT_RCU */ +#ifdef CONFIG_TREE_PREEMPT_RCU + struct rcu_node *rcu_blocked_node; #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT) @@ -1740,7 +1742,7 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t * #define tsk_used_math(p) ((p)->flags & PF_USED_MATH) #define used_math() tsk_used_math(current) -#ifdef CONFIG_TREE_PREEMPT_RCU +#ifdef CONFIG_PREEMPT_RCU #define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */ #define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */ @@ -1749,7 +1751,9 @@ static inline void rcu_copy_process(struct task_struct *p) { p->rcu_read_lock_nesting = 0; p->rcu_read_unlock_special = 0; +#ifdef CONFIG_TREE_PREEMPT_RCU p->rcu_blocked_node = NULL; +#endif INIT_LIST_HEAD(&p->rcu_node_entry); } diff --git a/init/Kconfig b/init/Kconfig index dbc08baad77e..a619a1ac7f4c 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -348,7 +348,7 @@ config TREE_RCU smaller systems. config TREE_PREEMPT_RCU - bool "Preemptable tree-based hierarchical RCU" + bool "Preemptible tree-based hierarchical RCU" depends on PREEMPT help This option selects the RCU implementation that is @@ -366,8 +366,22 @@ config TINY_RCU is not required. This option greatly reduces the memory footprint of RCU. +config TINY_PREEMPT_RCU + bool "Preemptible UP-only small-memory-footprint RCU" + depends on !SMP && PREEMPT + help + This option selects the RCU implementation that is designed + for real-time UP systems. This option greatly reduces the + memory footprint of RCU. + endchoice +config PREEMPT_RCU + def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU ) + help + This option enables preemptible-RCU code that is common between + the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations. + config RCU_TRACE bool "Enable tracing for RCU" depends on TREE_RCU || TREE_PREEMPT_RCU diff --git a/kernel/Makefile b/kernel/Makefile index 0b72d1a74be0..17046b6e7c90 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -86,6 +86,7 @@ obj-$(CONFIG_TREE_RCU) += rcutree.o obj-$(CONFIG_TREE_PREEMPT_RCU) += rcutree.o obj-$(CONFIG_TREE_RCU_TRACE) += rcutree_trace.o obj-$(CONFIG_TINY_RCU) += rcutiny.o +obj-$(CONFIG_TINY_PREEMPT_RCU) += rcutiny.o obj-$(CONFIG_RELAY) += relay.o obj-$(CONFIG_SYSCTL) += utsname_sysctl.o obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 196ec02f8be0..d806735342ac 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -59,6 +59,14 @@ int rcu_scheduler_active __read_mostly; EXPORT_SYMBOL_GPL(rcu_scheduler_active); #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ +/* Forward declarations for rcutiny_plugin.h. */ +static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp); +static void __call_rcu(struct rcu_head *head, + void (*func)(struct rcu_head *rcu), + struct rcu_ctrlblk *rcp); + +#include "rcutiny_plugin.h" + #ifdef CONFIG_NO_HZ static long rcu_dynticks_nesting = 1; @@ -140,6 +148,7 @@ void rcu_check_callbacks(int cpu, int user) rcu_sched_qs(cpu); else if (!in_softirq()) rcu_bh_qs(cpu); + rcu_preempt_check_callbacks(); } /* @@ -162,6 +171,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) *rcp->donetail = NULL; if (rcp->curtail == rcp->donetail) rcp->curtail = &rcp->rcucblist; + rcu_preempt_remove_callbacks(rcp); rcp->donetail = &rcp->rcucblist; local_irq_restore(flags); @@ -182,6 +192,7 @@ static void rcu_process_callbacks(struct softirq_action *unused) { __rcu_process_callbacks(&rcu_sched_ctrlblk); __rcu_process_callbacks(&rcu_bh_ctrlblk); + rcu_preempt_process_callbacks(); } /* @@ -223,15 +234,15 @@ static void __call_rcu(struct rcu_head *head, } /* - * Post an RCU callback to be invoked after the end of an RCU grace + * Post an RCU callback to be invoked after the end of an RCU-sched grace * period. But since we have but one CPU, that would be after any * quiescent state. */ -void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) +void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_sched_ctrlblk); } -EXPORT_SYMBOL_GPL(call_rcu); +EXPORT_SYMBOL_GPL(call_rcu_sched); /* * Post an RCU bottom-half callback to be invoked after any subsequent @@ -243,20 +254,6 @@ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) } EXPORT_SYMBOL_GPL(call_rcu_bh); -void rcu_barrier(void) -{ - struct rcu_synchronize rcu; - - init_rcu_head_on_stack(&rcu.head); - init_completion(&rcu.completion); - /* Will wake me after RCU finished. */ - call_rcu(&rcu.head, wakeme_after_rcu); - /* Wait for it. */ - wait_for_completion(&rcu.completion); - destroy_rcu_head_on_stack(&rcu.head); -} -EXPORT_SYMBOL_GPL(rcu_barrier); - void rcu_barrier_bh(void) { struct rcu_synchronize rcu; @@ -289,5 +286,3 @@ void __init rcu_init(void) { open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); } - -#include "rcutiny_plugin.h" diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index d223a92bc742..e6bc1b447c6c 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -1,7 +1,7 @@ /* - * Read-Copy Update mechanism for mutual exclusion (tree-based version) + * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition * Internal non-public definitions that provide either classic - * or preemptable semantics. + * or preemptible semantics. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by @@ -17,11 +17,587 @@ * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * - * Copyright IBM Corporation, 2009 + * Copyright (c) 2010 Linaro * * Author: Paul E. McKenney */ +#ifdef CONFIG_TINY_PREEMPT_RCU + +#include + +/* FIXME: merge with definitions in kernel/rcutree.h. */ +#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) +#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) + +/* Global control variables for preemptible RCU. */ +struct rcu_preempt_ctrlblk { + struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */ + struct rcu_head **nexttail; + /* Tasks blocked in a preemptible RCU */ + /* read-side critical section while an */ + /* preemptible-RCU grace period is in */ + /* progress must wait for a later grace */ + /* period. This pointer points to the */ + /* ->next pointer of the last task that */ + /* must wait for a later grace period, or */ + /* to &->rcb.rcucblist if there is no */ + /* such task. */ + struct list_head blkd_tasks; + /* Tasks blocked in RCU read-side critical */ + /* section. Tasks are placed at the head */ + /* of this list and age towards the tail. */ + struct list_head *gp_tasks; + /* Pointer to the first task blocking the */ + /* current grace period, or NULL if there */ + /* is not such task. */ + struct list_head *exp_tasks; + /* Pointer to first task blocking the */ + /* current expedited grace period, or NULL */ + /* if there is no such task. If there */ + /* is no current expedited grace period, */ + /* then there cannot be any such task. */ + u8 gpnum; /* Current grace period. */ + u8 gpcpu; /* Last grace period blocked by the CPU. */ + u8 completed; /* Last grace period completed. */ + /* If all three are equal, RCU is idle. */ +}; + +static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = { + .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist, + .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist, + .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist, + .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks), +}; + +static int rcu_preempted_readers_exp(void); +static void rcu_report_exp_done(void); + +/* + * Return true if the CPU has not yet responded to the current grace period. + */ +static int rcu_cpu_cur_gp(void) +{ + return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum; +} + +/* + * Check for a running RCU reader. Because there is only one CPU, + * there can be but one running RCU reader at a time. ;-) + */ +static int rcu_preempt_running_reader(void) +{ + return current->rcu_read_lock_nesting; +} + +/* + * Check for preempted RCU readers blocking any grace period. + * If the caller needs a reliable answer, it must disable hard irqs. + */ +static int rcu_preempt_blocked_readers_any(void) +{ + return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks); +} + +/* + * Check for preempted RCU readers blocking the current grace period. + * If the caller needs a reliable answer, it must disable hard irqs. + */ +static int rcu_preempt_blocked_readers_cgp(void) +{ + return rcu_preempt_ctrlblk.gp_tasks != NULL; +} + +/* + * Return true if another preemptible-RCU grace period is needed. + */ +static int rcu_preempt_needs_another_gp(void) +{ + return *rcu_preempt_ctrlblk.rcb.curtail != NULL; +} + +/* + * Return true if a preemptible-RCU grace period is in progress. + * The caller must disable hardirqs. + */ +static int rcu_preempt_gp_in_progress(void) +{ + return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum; +} + +/* + * Record a preemptible-RCU quiescent state for the specified CPU. Note + * that this just means that the task currently running on the CPU is + * in a quiescent state. There might be any number of tasks blocked + * while in an RCU read-side critical section. + * + * Unlike the other rcu_*_qs() functions, callers to this function + * must disable irqs in order to protect the assignment to + * ->rcu_read_unlock_special. + * + * Because this is a single-CPU implementation, the only way a grace + * period can end is if the CPU is in a quiescent state. The reason is + * that a blocked preemptible-RCU reader can exit its critical section + * only if the CPU is running it at the time. Therefore, when the + * last task blocking the current grace period exits its RCU read-side + * critical section, neither the CPU nor blocked tasks will be stopping + * the current grace period. (In contrast, SMP implementations + * might have CPUs running in RCU read-side critical sections that + * block later grace periods -- but this is not possible given only + * one CPU.) + */ +static void rcu_preempt_cpu_qs(void) +{ + /* Record both CPU and task as having responded to current GP. */ + rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum; + current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; + + /* + * If there is no GP, or if blocked readers are still blocking GP, + * then there is nothing more to do. + */ + if (!rcu_preempt_gp_in_progress() || rcu_preempt_blocked_readers_cgp()) + return; + + /* Advance callbacks. */ + rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum; + rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail; + rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail; + + /* If there are no blocked readers, next GP is done instantly. */ + if (!rcu_preempt_blocked_readers_any()) + rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail; + + /* If there are done callbacks, make RCU_SOFTIRQ process them. */ + if (*rcu_preempt_ctrlblk.rcb.donetail != NULL) + raise_softirq(RCU_SOFTIRQ); +} + +/* + * Start a new RCU grace period if warranted. Hard irqs must be disabled. + */ +static void rcu_preempt_start_gp(void) +{ + if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) { + + /* Official start of GP. */ + rcu_preempt_ctrlblk.gpnum++; + + /* Any blocked RCU readers block new GP. */ + if (rcu_preempt_blocked_readers_any()) + rcu_preempt_ctrlblk.gp_tasks = + rcu_preempt_ctrlblk.blkd_tasks.next; + + /* If there is no running reader, CPU is done with GP. */ + if (!rcu_preempt_running_reader()) + rcu_preempt_cpu_qs(); + } +} + +/* + * We have entered the scheduler, and the current task might soon be + * context-switched away from. If this task is in an RCU read-side + * critical section, we will no longer be able to rely on the CPU to + * record that fact, so we enqueue the task on the blkd_tasks list. + * If the task started after the current grace period began, as recorded + * by ->gpcpu, we enqueue at the beginning of the list. Otherwise + * before the element referenced by ->gp_tasks (or at the tail if + * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element. + * The task will dequeue itself when it exits the outermost enclosing + * RCU read-side critical section. Therefore, the current grace period + * cannot be permitted to complete until the ->gp_tasks pointer becomes + * NULL. + * + * Caller must disable preemption. + */ +void rcu_preempt_note_context_switch(void) +{ + struct task_struct *t = current; + unsigned long flags; + + local_irq_save(flags); /* must exclude scheduler_tick(). */ + if (rcu_preempt_running_reader() && + (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { + + /* Possibly blocking in an RCU read-side critical section. */ + t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; + + /* + * If this CPU has already checked in, then this task + * will hold up the next grace period rather than the + * current grace period. Queue the task accordingly. + * If the task is queued for the current grace period + * (i.e., this CPU has not yet passed through a quiescent + * state for the current grace period), then as long + * as that task remains queued, the current grace period + * cannot end. + */ + list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks); + if (rcu_cpu_cur_gp()) + rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry; + } + + /* + * Either we were not in an RCU read-side critical section to + * begin with, or we have now recorded that critical section + * globally. Either way, we can now note a quiescent state + * for this CPU. Again, if we were in an RCU read-side critical + * section, and if that critical section was blocking the current + * grace period, then the fact that the task has been enqueued + * means that current grace period continues to be blocked. + */ + rcu_preempt_cpu_qs(); + local_irq_restore(flags); +} + +/* + * Tiny-preemptible RCU implementation for rcu_read_lock(). + * Just increment ->rcu_read_lock_nesting, shared state will be updated + * if we block. + */ +void __rcu_read_lock(void) +{ + current->rcu_read_lock_nesting++; + barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */ +} +EXPORT_SYMBOL_GPL(__rcu_read_lock); + +/* + * Handle special cases during rcu_read_unlock(), such as needing to + * notify RCU core processing or task having blocked during the RCU + * read-side critical section. + */ +static void rcu_read_unlock_special(struct task_struct *t) +{ + int empty; + int empty_exp; + unsigned long flags; + struct list_head *np; + int special; + + /* + * NMI handlers cannot block and cannot safely manipulate state. + * They therefore cannot possibly be special, so just leave. + */ + if (in_nmi()) + return; + + local_irq_save(flags); + + /* + * If RCU core is waiting for this CPU to exit critical section, + * let it know that we have done so. + */ + special = t->rcu_read_unlock_special; + if (special & RCU_READ_UNLOCK_NEED_QS) + rcu_preempt_cpu_qs(); + + /* Hardware IRQ handlers cannot block. */ + if (in_irq()) { + local_irq_restore(flags); + return; + } + + /* Clean up if blocked during RCU read-side critical section. */ + if (special & RCU_READ_UNLOCK_BLOCKED) { + t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; + + /* + * Remove this task from the ->blkd_tasks list and adjust + * any pointers that might have been referencing it. + */ + empty = !rcu_preempt_blocked_readers_cgp(); + empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL; + np = t->rcu_node_entry.next; + if (np == &rcu_preempt_ctrlblk.blkd_tasks) + np = NULL; + list_del(&t->rcu_node_entry); + if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks) + rcu_preempt_ctrlblk.gp_tasks = np; + if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks) + rcu_preempt_ctrlblk.exp_tasks = np; + INIT_LIST_HEAD(&t->rcu_node_entry); + + /* + * If this was the last task on the current list, and if + * we aren't waiting on the CPU, report the quiescent state + * and start a new grace period if needed. + */ + if (!empty && !rcu_preempt_blocked_readers_cgp()) { + rcu_preempt_cpu_qs(); + rcu_preempt_start_gp(); + } + + /* + * If this was the last task on the expedited lists, + * then we need wake up the waiting task. + */ + if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL) + rcu_report_exp_done(); + } + local_irq_restore(flags); +} + +/* + * Tiny-preemptible RCU implementation for rcu_read_unlock(). + * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost + * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then + * invoke rcu_read_unlock_special() to clean up after a context switch + * in an RCU read-side critical section and other special cases. + */ +void __rcu_read_unlock(void) +{ + struct task_struct *t = current; + + barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */ + --t->rcu_read_lock_nesting; + barrier(); /* decrement before load of ->rcu_read_unlock_special */ + if (t->rcu_read_lock_nesting == 0 && + unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) + rcu_read_unlock_special(t); +#ifdef CONFIG_PROVE_LOCKING + WARN_ON_ONCE(t->rcu_read_lock_nesting < 0); +#endif /* #ifdef CONFIG_PROVE_LOCKING */ +} +EXPORT_SYMBOL_GPL(__rcu_read_unlock); + +/* + * Check for a quiescent state from the current CPU. When a task blocks, + * the task is recorded in the rcu_preempt_ctrlblk structure, which is + * checked elsewhere. This is called from the scheduling-clock interrupt. + * + * Caller must disable hard irqs. + */ +static void rcu_preempt_check_callbacks(void) +{ + struct task_struct *t = current; + + if (!rcu_preempt_running_reader() && rcu_preempt_gp_in_progress()) + rcu_preempt_cpu_qs(); + if (&rcu_preempt_ctrlblk.rcb.rcucblist != + rcu_preempt_ctrlblk.rcb.donetail) + raise_softirq(RCU_SOFTIRQ); + if (rcu_preempt_gp_in_progress() && rcu_preempt_running_reader()) + t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; +} + +/* + * TINY_PREEMPT_RCU has an extra callback-list tail pointer to + * update, so this is invoked from __rcu_process_callbacks() to + * handle that case. Of course, it is invoked for all flavors of + * RCU, but RCU callbacks can appear only on one of the lists, and + * neither ->nexttail nor ->donetail can possibly be NULL, so there + * is no need for an explicit check. + */ +static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) +{ + if (rcu_preempt_ctrlblk.nexttail == rcp->donetail) + rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist; +} + +/* + * Process callbacks for preemptible RCU. + */ +static void rcu_preempt_process_callbacks(void) +{ + __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb); +} + +/* + * Queue a preemptible -RCU callback for invocation after a grace period. + */ +void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) +{ + unsigned long flags; + + debug_rcu_head_queue(head); + head->func = func; + head->next = NULL; + + local_irq_save(flags); + *rcu_preempt_ctrlblk.nexttail = head; + rcu_preempt_ctrlblk.nexttail = &head->next; + rcu_preempt_start_gp(); /* checks to see if GP needed. */ + local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(call_rcu); + +void rcu_barrier(void) +{ + struct rcu_synchronize rcu; + + init_rcu_head_on_stack(&rcu.head); + init_completion(&rcu.completion); + /* Will wake me after RCU finished. */ + call_rcu(&rcu.head, wakeme_after_rcu); + /* Wait for it. */ + wait_for_completion(&rcu.completion); + destroy_rcu_head_on_stack(&rcu.head); +} +EXPORT_SYMBOL_GPL(rcu_barrier); + +/* + * synchronize_rcu - wait until a grace period has elapsed. + * + * Control will return to the caller some time after a full grace + * period has elapsed, in other words after all currently executing RCU + * read-side critical sections have completed. RCU read-side critical + * sections are delimited by rcu_read_lock() and rcu_read_unlock(), + * and may be nested. + */ +void synchronize_rcu(void) +{ +#ifdef CONFIG_DEBUG_LOCK_ALLOC + if (!rcu_scheduler_active) + return; +#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ + + WARN_ON_ONCE(rcu_preempt_running_reader()); + if (!rcu_preempt_blocked_readers_any()) + return; + + /* Once we get past the fastpath checks, same code as rcu_barrier(). */ + rcu_barrier(); +} +EXPORT_SYMBOL_GPL(synchronize_rcu); + +static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); +static unsigned long sync_rcu_preempt_exp_count; +static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); + +/* + * Return non-zero if there are any tasks in RCU read-side critical + * sections blocking the current preemptible-RCU expedited grace period. + * If there is no preemptible-RCU expedited grace period currently in + * progress, returns zero unconditionally. + */ +static int rcu_preempted_readers_exp(void) +{ + return rcu_preempt_ctrlblk.exp_tasks != NULL; +} + +/* + * Report the exit from RCU read-side critical section for the last task + * that queued itself during or before the current expedited preemptible-RCU + * grace period. + */ +static void rcu_report_exp_done(void) +{ + wake_up(&sync_rcu_preempt_exp_wq); +} + +/* + * Wait for an rcu-preempt grace period, but expedite it. The basic idea + * is to rely in the fact that there is but one CPU, and that it is + * illegal for a task to invoke synchronize_rcu_expedited() while in a + * preemptible-RCU read-side critical section. Therefore, any such + * critical sections must correspond to blocked tasks, which must therefore + * be on the ->blkd_tasks list. So just record the current head of the + * list in the ->exp_tasks pointer, and wait for all tasks including and + * after the task pointed to by ->exp_tasks to drain. + */ +void synchronize_rcu_expedited(void) +{ + unsigned long flags; + struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk; + unsigned long snap; + + barrier(); /* ensure prior action seen before grace period. */ + + WARN_ON_ONCE(rcu_preempt_running_reader()); + + /* + * Acquire lock so that there is only one preemptible RCU grace + * period in flight. Of course, if someone does the expedited + * grace period for us while we are acquiring the lock, just leave. + */ + snap = sync_rcu_preempt_exp_count + 1; + mutex_lock(&sync_rcu_preempt_exp_mutex); + if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count)) + goto unlock_mb_ret; /* Others did our work for us. */ + + local_irq_save(flags); + + /* + * All RCU readers have to already be on blkd_tasks because + * we cannot legally be executing in an RCU read-side critical + * section. + */ + + /* Snapshot current head of ->blkd_tasks list. */ + rpcp->exp_tasks = rpcp->blkd_tasks.next; + if (rpcp->exp_tasks == &rpcp->blkd_tasks) + rpcp->exp_tasks = NULL; + local_irq_restore(flags); + + /* Wait for tail of ->blkd_tasks list to drain. */ + if (rcu_preempted_readers_exp()) + wait_event(sync_rcu_preempt_exp_wq, + !rcu_preempted_readers_exp()); + + /* Clean up and exit. */ + barrier(); /* ensure expedited GP seen before counter increment. */ + sync_rcu_preempt_exp_count++; +unlock_mb_ret: + mutex_unlock(&sync_rcu_preempt_exp_mutex); + barrier(); /* ensure subsequent action seen after grace period. */ +} +EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); + +/* + * Does preemptible RCU need the CPU to stay out of dynticks mode? + */ +int rcu_preempt_needs_cpu(void) +{ + if (!rcu_preempt_running_reader()) + rcu_preempt_cpu_qs(); + return rcu_preempt_ctrlblk.rcb.rcucblist != NULL; +} + +/* + * Check for a task exiting while in a preemptible -RCU read-side + * critical section, clean up if so. No need to issue warnings, + * as debug_check_no_locks_held() already does this if lockdep + * is enabled. + */ +void exit_rcu(void) +{ + struct task_struct *t = current; + + if (t->rcu_read_lock_nesting == 0) + return; + t->rcu_read_lock_nesting = 1; + rcu_read_unlock(); +} + +#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */ + +/* + * Because preemptible RCU does not exist, it never has any callbacks + * to check. + */ +static void rcu_preempt_check_callbacks(void) +{ +} + +/* + * Because preemptible RCU does not exist, it never has any callbacks + * to remove. + */ +static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) +{ +} + +/* + * Because preemptible RCU does not exist, it never has any callbacks + * to process. + */ +static void rcu_preempt_process_callbacks(void) +{ +} + +#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */ + #ifdef CONFIG_DEBUG_LOCK_ALLOC #include From 9079fd7c2e06a92cf27d05224a1f478581916c5b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 7 Aug 2010 21:59:54 -0700 Subject: [PATCH 30/52] rcu: update obsolete rcu_read_lock() comment. The comment says that blocking is illegal in rcu_read_lock()-style RCU read-side critical sections, which is no longer entirely true given preemptible RCU. This commit provides a fix. Suggested-by: David Miller Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 24b896649384..d7af96ef6fcf 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -458,7 +458,20 @@ extern int rcu_my_thread_group_empty(void); * will be deferred until the outermost RCU read-side critical section * completes. * - * It is illegal to block while in an RCU read-side critical section. + * You can avoid reading and understanding the next paragraph by + * following this rule: don't put anything in an rcu_read_lock() RCU + * read-side critical section that would block in a !PREEMPT kernel. + * But if you want the full story, read on! + * + * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it + * is illegal to block while in an RCU read-side critical section. In + * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) + * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may + * be preempted, but explicit blocking is illegal. Finally, in preemptible + * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, + * RCU read-side critical sections may be preempted and they may also + * block, but only when acquiring spinlocks that are subject to priority + * inheritance. */ static inline void rcu_read_lock(void) { From 8cdd32a918350430483751feaae1c19cef816f69 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 9 Aug 2010 14:23:03 -0700 Subject: [PATCH 31/52] rcu: refer RCU CPU stall-warning victims to stallwarn.txt There is some documentation on RCU CPU stall warnings contained in Documentation/RCU/stallwarn.txt, but it will not be apparent to someone who runs into such a warning while under time pressure. This commit therefore adds comments preceding the printk()s pointing out the location of this documentation. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 5aab7dabd0d5..ff214118e4b8 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -487,8 +487,11 @@ static void print_other_cpu_stall(struct rcu_state *rsp) rcu_print_task_stall(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); - /* OK, time to rat on our buddy... */ - + /* + * OK, time to rat on our buddy... + * See Documentation/RCU/stallwarn.txt for info on how to debug + * RCU CPU stall warnings. + */ printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks: {", rsp->name); rcu_for_each_leaf_node(rsp, rnp) { @@ -517,6 +520,11 @@ static void print_cpu_stall(struct rcu_state *rsp) unsigned long flags; struct rcu_node *rnp = rcu_get_root(rsp); + /* + * OK, time to rat on ourselves... + * See Documentation/RCU/stallwarn.txt for info on how to debug + * RCU CPU stall warnings. + */ printk(KERN_ERR "INFO: %s detected stall on CPU %d (t=%lu jiffies)\n", rsp->name, smp_processor_id(), jiffies - rsp->gp_start); trigger_all_cpu_backtrace(); From 53d84e004d5e8c018be395c4330dc72fd60bd13e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 10 Aug 2010 14:28:53 -0700 Subject: [PATCH 32/52] rcu: permit suppressing current grace period's CPU stall warnings When using a kernel debugger, a long sojourn in the debugger can get you lots of RCU CPU stall warnings once you resume. This might not be helpful, especially if you are using the system console. This patch therefore allows RCU CPU stall warnings to be suppressed, but only for the duration of the current set of grace periods. This differs from Jason's original patch in that it adds support for tiny RCU and preemptible RCU, and uses a slightly different method for suppressing the RCU CPU stall warning messages. Signed-off-by: Jason Wessel Signed-off-by: Paul E. McKenney Tested-by: Jason Wessel --- include/linux/rcutiny.h | 4 ++++ include/linux/rcutree.h | 1 + kernel/rcutree.c | 20 ++++++++++++++++++++ kernel/rcutree.h | 1 + kernel/rcutree_plugin.h | 18 ++++++++++++++++++ 5 files changed, 44 insertions(+) diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 4cc5eba41616..3fa179784e18 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -178,6 +178,10 @@ static inline void rcu_sched_force_quiescent_state(void) { } +static inline void rcu_cpu_stall_reset(void) +{ +} + #ifdef CONFIG_DEBUG_LOCK_ALLOC extern int rcu_scheduler_active __read_mostly; diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index c13b85dd22bc..0726809497ba 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -36,6 +36,7 @@ extern void rcu_sched_qs(int cpu); extern void rcu_bh_qs(int cpu); extern void rcu_note_context_switch(int cpu); extern int rcu_needs_cpu(int cpu); +extern void rcu_cpu_stall_reset(void); #ifdef CONFIG_TREE_PREEMPT_RCU diff --git a/kernel/rcutree.c b/kernel/rcutree.c index ff214118e4b8..42140a860bb9 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -565,6 +565,22 @@ static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) return NOTIFY_DONE; } +/** + * rcu_cpu_stall_reset - prevent further stall warnings in current grace period + * + * Set the stall-warning timeout way off into the future, thus preventing + * any RCU CPU stall-warning messages from appearing in the current set of + * RCU grace periods. + * + * The caller must disable hard irqs. + */ +void rcu_cpu_stall_reset(void) +{ + rcu_sched_state.jiffies_stall = jiffies + ULONG_MAX / 2; + rcu_bh_state.jiffies_stall = jiffies + ULONG_MAX / 2; + rcu_preempt_stall_reset(); +} + static struct notifier_block rcu_panic_block = { .notifier_call = rcu_panic, }; @@ -584,6 +600,10 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) { } +void rcu_cpu_stall_reset(void) +{ +} + static void __init check_cpu_stall_init(void) { } diff --git a/kernel/rcutree.h b/kernel/rcutree.h index bb4d08695c45..7abd439a7573 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -372,6 +372,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, #ifdef CONFIG_RCU_CPU_STALL_DETECTOR static void rcu_print_detail_task_stall(struct rcu_state *rsp); static void rcu_print_task_stall(struct rcu_node *rnp); +static void rcu_preempt_stall_reset(void); #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp); #ifdef CONFIG_HOTPLUG_CPU diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 63bb7714fdeb..561410f70d4a 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -417,6 +417,16 @@ static void rcu_print_task_stall(struct rcu_node *rnp) } } +/* + * Suppress preemptible RCU's CPU stall warnings by pushing the + * time of the next stall-warning message comfortably far into the + * future. + */ +static void rcu_preempt_stall_reset(void) +{ + rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2; +} + #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ /* @@ -867,6 +877,14 @@ static void rcu_print_task_stall(struct rcu_node *rnp) { } +/* + * Because preemptible RCU does not exist, there is no need to suppress + * its CPU stall warnings. + */ +static void rcu_preempt_stall_reset(void) +{ +} + #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ /* From a3dc3fb161f9b4066c0fce22db72638af8baf83b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 13 Aug 2010 16:16:25 -0700 Subject: [PATCH 33/52] rcu: repair code-duplication FIXMEs Combine the duplicate definitions of ULONG_CMP_GE(), ULONG_CMP_LT(), and rcu_preempt_depth() into include/linux/rcupdate.h. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 15 +++++++++++++++ include/linux/rcutiny.h | 7 ------- include/linux/rcutree.h | 6 ------ kernel/rcutiny_plugin.h | 4 ---- kernel/rcutree.h | 3 --- 5 files changed, 15 insertions(+), 20 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index d7af96ef6fcf..325bad7bbca9 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -47,6 +47,9 @@ extern int rcutorture_runnable; /* for sysctl */ #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ +#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) +#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) + /** * struct rcu_head - callback structure for use with RCU * @next: next update requests in a list @@ -66,6 +69,18 @@ extern int sched_expedited_torture_stats(char *page); /* Internal to kernel */ extern void rcu_init(void); +#ifdef CONFIG_PREEMPT_RCU + +/* + * Defined as a macro as it is a very low level header included from + * areas that don't even know about current. This gives the rcu_read_lock() + * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other + * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. + */ +#define rcu_preempt_depth() (current->rcu_read_lock_nesting) + +#endif /* #ifdef CONFIG_PREEMPT_RCU */ + #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) #include #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 3fa179784e18..c6b11dc5ba0a 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -133,13 +133,6 @@ static inline int rcu_needs_cpu(int cpu) return rcu_preempt_needs_cpu(); } -/* - * Defined as macro as it is a very low level header - * included from areas that don't even know about current - * FIXME: combine with include/linux/rcutree.h into rcupdate.h. - */ -#define rcu_preempt_depth() (current->rcu_read_lock_nesting) - #endif /* #else #ifdef CONFIG_TINY_RCU */ static inline void rcu_note_context_switch(int cpu) diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 0726809497ba..54a20c11f98d 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -45,12 +45,6 @@ extern void __rcu_read_unlock(void); extern void synchronize_rcu(void); extern void exit_rcu(void); -/* - * Defined as macro as it is a very low level header - * included from areas that don't even know about current - */ -#define rcu_preempt_depth() (current->rcu_read_lock_nesting) - #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ static inline void __rcu_read_lock(void) diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index e6bc1b447c6c..c5bea1137dcb 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -26,10 +26,6 @@ #include -/* FIXME: merge with definitions in kernel/rcutree.h. */ -#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) -#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) - /* Global control variables for preemptible RCU. */ struct rcu_preempt_ctrlblk { struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */ diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 7abd439a7573..7918ba61873f 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -272,9 +272,6 @@ struct rcu_data { #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ -#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) -#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) - /* * RCU global state, including node hierarchy. This hierarchy is * represented in "heap" form in a dense array. The root (first level) From 5cc6517abdeccb6690b344a43b5ce8eaee82da3c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 13 Aug 2010 16:34:22 -0700 Subject: [PATCH 34/52] rcu: document ways of stalling updates in low-memory situations Signed-off-by: Paul E. McKenney --- Documentation/RCU/checklist.txt | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index c7c6788956f4..0c134f8afc6f 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -218,13 +218,22 @@ over a rather long period of time, but improvements are always welcome! include: a. Keeping a count of the number of data-structure elements - used by the RCU-protected data structure, including those - waiting for a grace period to elapse. Enforce a limit - on this number, stalling updates as needed to allow - previously deferred frees to complete. + used by the RCU-protected data structure, including + those waiting for a grace period to elapse. Enforce a + limit on this number, stalling updates as needed to allow + previously deferred frees to complete. Alternatively, + limit only the number awaiting deferred free rather than + the total number of elements. - Alternatively, limit only the number awaiting deferred - free rather than the total number of elements. + One way to stall the updates is to acquire the update-side + mutex. (Don't try this with a spinlock -- other CPUs + spinning on the lock could prevent the grace period + from ever ending.) Another way to stall the updates + is for the updates to use a wrapper function around + the memory allocator, so that this wrapper function + simulates OOM when there is too much memory awaiting an + RCU grace period. There are of course many other + variations on this theme. b. Limiting update rate. For example, if updates occur only once per hour, then no explicit rate limiting is required, From 73d4da4d360136826b36f78f5cf72b29da82c8a6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 16 Aug 2010 10:50:54 -0700 Subject: [PATCH 35/52] rcu: Upgrade srcu_read_lock() docbook about SRCU grace periods It is illegal to wait for an SRCU grace period while within the corresponding flavor of SRCU read-side critical section. Therefore, this commit updates the srcu_read_lock() docbook accordingly. Signed-off-by: Paul E. McKenney --- include/linux/srcu.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 6f456a720ff0..58971e891f48 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -139,7 +139,12 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp) * @sp: srcu_struct in which to register the new reader. * * Enter an SRCU read-side critical section. Note that SRCU read-side - * critical sections may be nested. + * critical sections may be nested. However, it is illegal to + * call anything that waits on an SRCU grace period for the same + * srcu_struct, whether directly or indirectly. Please note that + * one way to indirectly wait on an SRCU grace period is to acquire + * a mutex that is held elsewhere while calling synchronize_srcu() or + * synchronize_srcu_expedited(). */ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) { From 7b0b759b65247cbc66384a912be9acf8d4800636 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 17 Aug 2010 14:18:46 -0700 Subject: [PATCH 36/52] rcu: combine duplicate code, courtesy of CONFIG_PREEMPT_RCU The CONFIG_PREEMPT_RCU kernel configuration parameter was recently re-introduced, but as an indication of the type of RCU (preemptible vs. non-preemptible) instead of as selecting a given implementation. This commit uses CONFIG_PREEMPT_RCU to combine duplicate code from include/linux/rcutiny.h and include/linux/rcutree.h into include/linux/rcupdate.h. This commit also combines a few other pieces of duplicate code that have accumulated. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 75 ++++++++++++++++++++++++++++++++++++++-- include/linux/rcutiny.h | 51 --------------------------- include/linux/rcutree.h | 50 --------------------------- kernel/rcutree_plugin.h | 9 ----- 4 files changed, 72 insertions(+), 113 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 325bad7bbca9..89414d67d961 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -61,16 +61,30 @@ struct rcu_head { }; /* Exported common interfaces */ +extern void call_rcu_sched(struct rcu_head *head, + void (*func)(struct rcu_head *rcu)); +extern void synchronize_sched(void); extern void rcu_barrier_bh(void); extern void rcu_barrier_sched(void); extern void synchronize_sched_expedited(void); extern int sched_expedited_torture_stats(char *page); -/* Internal to kernel */ -extern void rcu_init(void); +static inline void __rcu_read_lock_bh(void) +{ + local_bh_disable(); +} + +static inline void __rcu_read_unlock_bh(void) +{ + local_bh_enable(); +} #ifdef CONFIG_PREEMPT_RCU +extern void __rcu_read_lock(void); +extern void __rcu_read_unlock(void); +void synchronize_rcu(void); + /* * Defined as a macro as it is a very low level header included from * areas that don't even know about current. This gives the rcu_read_lock() @@ -79,7 +93,53 @@ extern void rcu_init(void); */ #define rcu_preempt_depth() (current->rcu_read_lock_nesting) -#endif /* #ifdef CONFIG_PREEMPT_RCU */ +#else /* #ifdef CONFIG_PREEMPT_RCU */ + +static inline void __rcu_read_lock(void) +{ + preempt_disable(); +} + +static inline void __rcu_read_unlock(void) +{ + preempt_enable(); +} + +static inline void synchronize_rcu(void) +{ + synchronize_sched(); +} + +static inline int rcu_preempt_depth(void) +{ + return 0; +} + +#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ + +/* Internal to kernel */ +extern void rcu_init(void); +extern void rcu_sched_qs(int cpu); +extern void rcu_bh_qs(int cpu); +extern void rcu_check_callbacks(int cpu, int user); +struct notifier_block; + +#ifdef CONFIG_NO_HZ + +extern void rcu_enter_nohz(void); +extern void rcu_exit_nohz(void); + +#else /* #ifdef CONFIG_NO_HZ */ + +static inline void rcu_enter_nohz(void) +{ +} + +static inline void rcu_exit_nohz(void) +{ +} + +#endif /* #else #ifdef CONFIG_NO_HZ */ #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) #include @@ -626,6 +686,8 @@ struct rcu_synchronize { extern void wakeme_after_rcu(struct rcu_head *head); +#ifdef CONFIG_PREEMPT_RCU + /** * call_rcu() - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. @@ -642,6 +704,13 @@ extern void wakeme_after_rcu(struct rcu_head *head); extern void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *head)); +#else /* #ifdef CONFIG_PREEMPT_RCU */ + +/* In classic RCU, call_rcu() is just call_rcu_sched(). */ +#define call_rcu call_rcu_sched + +#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ + /** * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. * @head: structure to be used for queueing the RCU updates. diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index c6b11dc5ba0a..13877cb93a60 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -27,34 +27,10 @@ #include -void rcu_sched_qs(int cpu); -void rcu_bh_qs(int cpu); - -#ifdef CONFIG_TINY_RCU -#define __rcu_read_lock() preempt_disable() -#define __rcu_read_unlock() preempt_enable() -#else /* #ifdef CONFIG_TINY_RCU */ -void __rcu_read_lock(void); -void __rcu_read_unlock(void); -#endif /* #else #ifdef CONFIG_TINY_RCU */ -#define __rcu_read_lock_bh() local_bh_disable() -#define __rcu_read_unlock_bh() local_bh_enable() -extern void call_rcu_sched(struct rcu_head *head, - void (*func)(struct rcu_head *rcu)); - #define rcu_init_sched() do { } while (0) -extern void synchronize_sched(void); - #ifdef CONFIG_TINY_RCU -#define call_rcu call_rcu_sched - -static inline void synchronize_rcu(void) -{ - synchronize_sched(); -} - static inline void synchronize_rcu_expedited(void) { synchronize_sched(); /* Only one CPU, so pretty fast anyway!!! */ @@ -67,7 +43,6 @@ static inline void rcu_barrier(void) #else /* #ifdef CONFIG_TINY_RCU */ -void synchronize_rcu(void); void rcu_barrier(void); void synchronize_rcu_expedited(void); @@ -83,25 +58,6 @@ static inline void synchronize_rcu_bh_expedited(void) synchronize_sched(); } -struct notifier_block; - -#ifdef CONFIG_NO_HZ - -extern void rcu_enter_nohz(void); -extern void rcu_exit_nohz(void); - -#else /* #ifdef CONFIG_NO_HZ */ - -static inline void rcu_enter_nohz(void) -{ -} - -static inline void rcu_exit_nohz(void) -{ -} - -#endif /* #else #ifdef CONFIG_NO_HZ */ - #ifdef CONFIG_TINY_RCU static inline void rcu_preempt_note_context_switch(void) @@ -117,11 +73,6 @@ static inline int rcu_needs_cpu(int cpu) return 0; } -static inline int rcu_preempt_depth(void) -{ - return 0; -} - #else /* #ifdef CONFIG_TINY_RCU */ void rcu_preempt_note_context_switch(void); @@ -141,8 +92,6 @@ static inline void rcu_note_context_switch(int cpu) rcu_preempt_note_context_switch(); } -extern void rcu_check_callbacks(int cpu, int user); - /* * Return the number of grace periods. */ diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 54a20c11f98d..95518e628794 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -30,59 +30,23 @@ #ifndef __LINUX_RCUTREE_H #define __LINUX_RCUTREE_H -struct notifier_block; - -extern void rcu_sched_qs(int cpu); -extern void rcu_bh_qs(int cpu); extern void rcu_note_context_switch(int cpu); extern int rcu_needs_cpu(int cpu); extern void rcu_cpu_stall_reset(void); #ifdef CONFIG_TREE_PREEMPT_RCU -extern void __rcu_read_lock(void); -extern void __rcu_read_unlock(void); -extern void synchronize_rcu(void); extern void exit_rcu(void); #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ -static inline void __rcu_read_lock(void) -{ - preempt_disable(); -} - -static inline void __rcu_read_unlock(void) -{ - preempt_enable(); -} - -#define synchronize_rcu synchronize_sched - static inline void exit_rcu(void) { } -static inline int rcu_preempt_depth(void) -{ - return 0; -} - #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ -static inline void __rcu_read_lock_bh(void) -{ - local_bh_disable(); -} -static inline void __rcu_read_unlock_bh(void) -{ - local_bh_enable(); -} - -extern void call_rcu_sched(struct rcu_head *head, - void (*func)(struct rcu_head *rcu)); extern void synchronize_rcu_bh(void); -extern void synchronize_sched(void); extern void synchronize_rcu_expedited(void); static inline void synchronize_rcu_bh_expedited(void) @@ -92,8 +56,6 @@ static inline void synchronize_rcu_bh_expedited(void) extern void rcu_barrier(void); -extern void rcu_check_callbacks(int cpu, int user); - extern long rcu_batches_completed(void); extern long rcu_batches_completed_bh(void); extern long rcu_batches_completed_sched(void); @@ -101,18 +63,6 @@ extern void rcu_force_quiescent_state(void); extern void rcu_bh_force_quiescent_state(void); extern void rcu_sched_force_quiescent_state(void); -#ifdef CONFIG_NO_HZ -void rcu_enter_nohz(void); -void rcu_exit_nohz(void); -#else /* CONFIG_NO_HZ */ -static inline void rcu_enter_nohz(void) -{ -} -static inline void rcu_exit_nohz(void) -{ -} -#endif /* CONFIG_NO_HZ */ - /* A context switch is a grace period for RCU-sched and RCU-bh. */ static inline int rcu_blocking_is_gp(void) { diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 561410f70d4a..87f60f06b18e 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -938,15 +938,6 @@ static void rcu_preempt_process_callbacks(void) { } -/* - * In classic RCU, call_rcu() is just call_rcu_sched(). - */ -void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) -{ - call_rcu_sched(head, func); -} -EXPORT_SYMBOL_GPL(call_rcu); - /* * Wait for an rcu-preempt grace period, but make it happen quickly. * But because preemptable RCU does not exist, map to rcu-sched. From 80dcf60e6b97c7363971e7a0a788d8484d35f8a6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 19 Aug 2010 16:57:45 -0700 Subject: [PATCH 37/52] rcu: apply TINY_PREEMPT_RCU read-side speedup to TREE_PREEMPT_RCU Replace one of the ACCESS_ONCE() calls in each of __rcu_read_lock() and __rcu_read_unlock() with barrier() as suggested by Steve Rostedt in order to avoid the potential compiler-optimization-induced bug noted by Mathieu Desnoyers. Located-by: Mathieu Desnoyers Suggested-by: Steven Rostedt Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 87f60f06b18e..e9e0bc74ff37 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -201,7 +201,7 @@ static void rcu_preempt_note_context_switch(int cpu) */ void __rcu_read_lock(void) { - ACCESS_ONCE(current->rcu_read_lock_nesting)++; + current->rcu_read_lock_nesting++; barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */ } EXPORT_SYMBOL_GPL(__rcu_read_lock); @@ -344,7 +344,9 @@ void __rcu_read_unlock(void) struct task_struct *t = current; barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ - if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 && + --t->rcu_read_lock_nesting; + barrier(); /* decrement before load of ->rcu_read_unlock_special */ + if (t->rcu_read_lock_nesting == 0 && unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) rcu_read_unlock_special(t); #ifdef CONFIG_PROVE_LOCKING From 65e6bf484c497f02d47a0faae69ee398cd59cfda Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 19 Aug 2010 21:43:09 -0700 Subject: [PATCH 38/52] rcu: add comment stating that list_empty() applies to RCU-protected lists Because list_empty() does not dereference any RCU-protected pointers, and further does not pass such pointers to the caller (so that the caller does not dereference them either), it is safe to use list_empty() on RCU-protected lists. There is no need for a list_empty_rcu(). This commit adds a comment stating this explicitly. Requested-by: Andrew Morton Signed-off-by: Paul E. McKenney --- include/linux/rculist.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index c10b1050dbe6..f31ef61f1c65 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -9,6 +9,15 @@ #include #include +/* + * Why is there no list_empty_rcu()? Because list_empty() serves this + * purpose. The list_empty() function fetches the RCU-protected pointer + * and compares it to the address of the list head, but neither dereferences + * this pointer itself nor provides this pointer to the caller. Therefore, + * it is not necessary to use rcu_dereference(), so that list_empty() can + * be used anywhere you would want to use a list_empty_rcu(). + */ + /* * return the ->next pointer of a list_head in an rcu safe * way, we must not access it directly From 28457ee69c473a903e51e26c7bcd6f1e9eceb93e Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Tue, 9 Mar 2010 19:24:45 +0100 Subject: [PATCH 39/52] vhost: add __rcu annotations Also add rcu_dereference_protected() for code paths where locks are held. Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: "Michael S. Tsirkin" --- drivers/vhost/net.c | 16 ++++++++++++---- drivers/vhost/vhost.c | 22 ++++++++++++++++------ drivers/vhost/vhost.h | 10 +++++++--- 3 files changed, 35 insertions(+), 13 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 29e850a7a2f9..1318ee008346 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -127,7 +127,10 @@ static void handle_tx(struct vhost_net *net) size_t len, total_len = 0; int err, wmem; size_t hdr_size; - struct socket *sock = rcu_dereference(vq->private_data); + struct socket *sock; + + sock = rcu_dereference_check(vq->private_data, + lockdep_is_held(&vq->mutex)); if (!sock) return; @@ -582,7 +585,10 @@ static void vhost_net_disable_vq(struct vhost_net *n, static void vhost_net_enable_vq(struct vhost_net *n, struct vhost_virtqueue *vq) { - struct socket *sock = vq->private_data; + struct socket *sock; + + sock = rcu_dereference_protected(vq->private_data, + lockdep_is_held(&vq->mutex)); if (!sock) return; if (vq == n->vqs + VHOST_NET_VQ_TX) { @@ -598,7 +604,8 @@ static struct socket *vhost_net_stop_vq(struct vhost_net *n, struct socket *sock; mutex_lock(&vq->mutex); - sock = vq->private_data; + sock = rcu_dereference_protected(vq->private_data, + lockdep_is_held(&vq->mutex)); vhost_net_disable_vq(n, vq); rcu_assign_pointer(vq->private_data, NULL); mutex_unlock(&vq->mutex); @@ -736,7 +743,8 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd) } /* start polling new socket */ - oldsock = vq->private_data; + oldsock = rcu_dereference_protected(vq->private_data, + lockdep_is_held(&vq->mutex)); if (sock != oldsock) { vhost_net_disable_vq(n, vq); rcu_assign_pointer(vq->private_data, sock); diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index e05557d52999..b5c49478d203 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -284,7 +284,7 @@ long vhost_dev_reset_owner(struct vhost_dev *dev) vhost_dev_cleanup(dev); memory->nregions = 0; - dev->memory = memory; + RCU_INIT_POINTER(dev->memory, memory); return 0; } @@ -316,8 +316,9 @@ void vhost_dev_cleanup(struct vhost_dev *dev) fput(dev->log_file); dev->log_file = NULL; /* No one will access memory at this point */ - kfree(dev->memory); - dev->memory = NULL; + kfree(rcu_dereference_protected(dev->memory, + lockdep_is_held(&dev->mutex))); + RCU_INIT_POINTER(dev->memory, NULL); if (dev->mm) mmput(dev->mm); dev->mm = NULL; @@ -401,14 +402,22 @@ static int vq_access_ok(unsigned int num, /* Caller should have device mutex but not vq mutex */ int vhost_log_access_ok(struct vhost_dev *dev) { - return memory_access_ok(dev, dev->memory, 1); + struct vhost_memory *mp; + + mp = rcu_dereference_protected(dev->memory, + lockdep_is_held(&dev->mutex)); + return memory_access_ok(dev, mp, 1); } /* Verify access for write logging. */ /* Caller should have vq mutex and device mutex */ static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user *log_base) { - return vq_memory_access_ok(log_base, vq->dev->memory, + struct vhost_memory *mp; + + mp = rcu_dereference_protected(vq->dev->memory, + lockdep_is_held(&vq->mutex)); + return vq_memory_access_ok(log_base, mp, vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) && (!vq->log_used || log_access_ok(log_base, vq->log_addr, sizeof *vq->used + @@ -448,7 +457,8 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m) kfree(newmem); return -EFAULT; } - oldmem = d->memory; + oldmem = rcu_dereference_protected(d->memory, + lockdep_is_held(&d->mutex)); rcu_assign_pointer(d->memory, newmem); synchronize_rcu(); kfree(oldmem); diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h index afd77295971c..af3c11ded5fd 100644 --- a/drivers/vhost/vhost.h +++ b/drivers/vhost/vhost.h @@ -106,7 +106,7 @@ struct vhost_virtqueue { * vhost_work execution acts instead of rcu_read_lock() and the end of * vhost_work execution acts instead of rcu_read_lock(). * Writers use virtqueue mutex. */ - void *private_data; + void __rcu *private_data; /* Log write descriptors */ void __user *log_base; struct vhost_log log[VHOST_NET_MAX_SG]; @@ -116,7 +116,7 @@ struct vhost_dev { /* Readers use RCU to access memory table pointer * log base pointer and features. * Writers use mutex below.*/ - struct vhost_memory *memory; + struct vhost_memory __rcu *memory; struct mm_struct *mm; struct mutex mutex; unsigned acked_features; @@ -173,7 +173,11 @@ enum { static inline int vhost_has_feature(struct vhost_dev *dev, int bit) { - unsigned acked_features = rcu_dereference(dev->acked_features); + unsigned acked_features; + + acked_features = + rcu_dereference_index_check(dev->acked_features, + lockdep_is_held(&dev->mutex)); return acked_features & (1 << bit); } From 2c96c7751d2bb822542b03ddfaca70933f5aaf02 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 23 Aug 2010 16:34:02 -0700 Subject: [PATCH 40/52] rcu: upgrade stallwarn.txt documentation for CPU-bound RT processes CPU-bound real-time processes can cause RCU CPU stall warnings, and much other trouble as well. Document the fact that they can cause RCU CPU stall warnings. Suggested-by: Darren Hart Signed-off-by: Paul E. McKenney --- Documentation/RCU/stallwarn.txt | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt index 44c6dcc93d6d..862c08ef1fde 100644 --- a/Documentation/RCU/stallwarn.txt +++ b/Documentation/RCU/stallwarn.txt @@ -80,6 +80,24 @@ o A CPU looping with bottom halves disabled. This condition can o For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel without invoking schedule(). +o A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might + happen to preempt a low-priority task in the middle of an RCU + read-side critical section. This is especially damaging if + that low-priority task is not permitted to run on any other CPU, + in which case the next RCU grace period can never complete, which + will eventually cause the system to run out of memory and hang. + While the system is in the process of running itself out of + memory, you might see stall-warning messages. + +o A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that + is running at a higher priority than the RCU softirq threads. + This will prevent RCU callbacks from ever being invoked, + and in a CONFIG_TREE_PREEMPT_RCU kernel will further prevent + RCU grace periods from ever completing. Either way, the + system will eventually run out of memory and hang. In the + CONFIG_TREE_PREEMPT_RCU case, you might see stall-warning + messages. + o A bug in the RCU implementation. o A hardware failure. This is quite unlikely, but has occurred From dd7c4d89730a1be2c1d361a8ae1f0fe9465ccf9c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 27 Aug 2010 10:51:17 -0700 Subject: [PATCH 41/52] rcu: performance fixes to TINY_PREEMPT_RCU callback checking This commit tightens up checks in rcu_preempt_check_callbacks() to avoid unnecessary special handling at rcu_read_unlock() time. Signed-off-by: Paul E. McKenney --- kernel/rcutiny_plugin.h | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index c5bea1137dcb..6ceca4f745ff 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -72,7 +72,7 @@ static void rcu_report_exp_done(void); /* * Return true if the CPU has not yet responded to the current grace period. */ -static int rcu_cpu_cur_gp(void) +static int rcu_cpu_blocking_cur_gp(void) { return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum; } @@ -229,7 +229,7 @@ void rcu_preempt_note_context_switch(void) * cannot end. */ list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks); - if (rcu_cpu_cur_gp()) + if (rcu_cpu_blocking_cur_gp()) rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry; } @@ -368,12 +368,16 @@ static void rcu_preempt_check_callbacks(void) { struct task_struct *t = current; - if (!rcu_preempt_running_reader() && rcu_preempt_gp_in_progress()) + if (rcu_preempt_gp_in_progress() && + (!rcu_preempt_running_reader() || + !rcu_cpu_blocking_cur_gp())) rcu_preempt_cpu_qs(); if (&rcu_preempt_ctrlblk.rcb.rcucblist != rcu_preempt_ctrlblk.rcb.donetail) raise_softirq(RCU_SOFTIRQ); - if (rcu_preempt_gp_in_progress() && rcu_preempt_running_reader()) + if (rcu_preempt_gp_in_progress() && + rcu_cpu_blocking_cur_gp() && + rcu_preempt_running_reader()) t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; } From 81a294c44e973dc7182e4733421b7cb2daba3c29 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 30 Aug 2010 09:52:50 -0700 Subject: [PATCH 42/52] rcu: fix _oddness handling of verbose stall warnings CONFIG_RCU_CPU_STALL_VERBOSE depends on CONFIG_TREE_PREEMPT_RCU, but rcu_bootup_announce_oddness() complains if CONFIG_RCU_CPU_STALL_VERBOSE is not set even in the case of CONFIG_TREE_RCU. This commit therefore fixes rcu_bootup_announce_oddness() to avoid insisting on impossibilities. Reported-by: Guy Martin Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index e9e0bc74ff37..71a4147473f9 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -57,7 +57,7 @@ static void __init rcu_bootup_announce_oddness(void) printk(KERN_INFO "\tRCU-based detection of stalled CPUs is disabled.\n"); #endif -#ifndef CONFIG_RCU_CPU_STALL_VERBOSE +#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n"); #endif #if NUM_RCU_LVL_4 != 0 From 829f8ed2c963df7c23d1c644db6c4387eb1601fa Mon Sep 17 00:00:00 2001 From: Christian Dietrich Date: Mon, 6 Sep 2010 16:37:12 +0200 Subject: [PATCH 43/52] kernel: Remove undead ifdef CONFIG_DEBUG_LOCK_ALLOC The CONFIG_DEBUG_LOCK_ALLOC ifdef isn't necessary at this point, because it is checked in an outer ifdef level already and has no effect here. Signed-off-by: Christian Dietrich Signed-off-by: Paul E. McKenney --- kernel/srcu.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/kernel/srcu.c b/kernel/srcu.c index 2980da3fd509..c71e07500536 100644 --- a/kernel/srcu.c +++ b/kernel/srcu.c @@ -46,11 +46,9 @@ static int init_srcu_struct_fields(struct srcu_struct *sp) int __init_srcu_struct(struct srcu_struct *sp, const char *name, struct lock_class_key *key) { -#ifdef CONFIG_DEBUG_LOCK_ALLOC /* Don't re-initialize a lock while it is held. */ debug_check_no_locks_freed((void *)sp, sizeof(*sp)); lockdep_init_map(&sp->dep_map, name, key, 0); -#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ return init_srcu_struct_fields(sp); } EXPORT_SYMBOL_GPL(__init_srcu_struct); From 53ecfba259f54b6967a35d19f4a564e3bc07997f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 13 Sep 2010 17:24:21 -0700 Subject: [PATCH 44/52] rcu: only one evaluation of arg in rcu_dereference_check() unless sparse The current version of the __rcu_access_pointer(), __rcu_dereference_check(), and __rcu_dereference_protected() macros evaluate their "p" argument three times, not counting typeof()s. This is bad news if that argument contains a side effect. This commit therefore evaluates this argument only once in normal kernel builds. However, the straightforward approach defeats sparse's RCU-pointer checking, so when __CHECKER__ is defined, the additional pair of evaluations of the "p" argument are performed in order to permit sparse to detect misuse of RCU-protected pointers. Signed-off-by: Paul E. McKenney Cc: Arnd Bergmann --- include/linux/rcupdate.h | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 89414d67d961..03cda7bed985 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -310,24 +310,32 @@ extern int rcu_my_thread_group_empty(void); * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in * the future. */ + +#ifdef __CHECKER__ +#define rcu_dereference_sparse(p, space) \ + ((void)(((typeof(*p) space *)p) == p)) +#else /* #ifdef __CHECKER__ */ +#define rcu_dereference_sparse(p, space) +#endif /* #else #ifdef __CHECKER__ */ + #define __rcu_access_pointer(p, space) \ ({ \ typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ - (void) (((typeof (*p) space *)p) == p); \ + rcu_dereference_sparse(p, space); \ ((typeof(*p) __force __kernel *)(_________p1)); \ }) #define __rcu_dereference_check(p, c, space) \ ({ \ typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ rcu_lockdep_assert(c); \ - (void) (((typeof (*p) space *)p) == p); \ + rcu_dereference_sparse(p, space); \ smp_read_barrier_depends(); \ ((typeof(*p) __force __kernel *)(_________p1)); \ }) #define __rcu_dereference_protected(p, c, space) \ ({ \ rcu_lockdep_assert(c); \ - (void) (((typeof (*p) space *)p) == p); \ + rcu_dereference_sparse(p, space); \ ((typeof(*p) __force __kernel *)(p)); \ }) From 0ddea0ead2ced99eaaaddff2beb755381e5c89f8 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 19 Sep 2010 21:06:14 -0700 Subject: [PATCH 45/52] rcu: fix sparse errors in rcutorture.c Add the sparse __rcu address-space identifier and make a couple of variables static. Signed-off-by: Paul E. McKenney --- kernel/rcutorture.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 729710273dcb..9d8e8fb2515f 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -120,7 +120,7 @@ struct rcu_torture { }; static LIST_HEAD(rcu_torture_freelist); -static struct rcu_torture *rcu_torture_current; +static struct rcu_torture __rcu *rcu_torture_current; static long rcu_torture_current_version; static struct rcu_torture rcu_tortures[10 * RCU_TORTURE_PIPE_LEN]; static DEFINE_SPINLOCK(rcu_torture_lock); @@ -153,8 +153,10 @@ int rcutorture_runnable = RCUTORTURE_RUNNABLE_INIT; #define FULLSTOP_SHUTDOWN 1 /* System shutdown with rcutorture running. */ #define FULLSTOP_RMMOD 2 /* Normal rmmod of rcutorture. */ static int fullstop = FULLSTOP_RMMOD; -DEFINE_MUTEX(fullstop_mutex); /* Protect fullstop transitions and spawning */ - /* of kthreads. */ +/* + * Protect fullstop transitions and spawning of kthreads. + */ +static DEFINE_MUTEX(fullstop_mutex); /* * Detect and respond to a system shutdown. @@ -737,7 +739,8 @@ rcu_torture_writer(void *arg) continue; rp->rtort_pipe_count = 0; udelay(rcu_random(&rand) & 0x3ff); - old_rp = rcu_torture_current; + old_rp = rcu_dereference_check(rcu_torture_current, + current == writer_task); rp->rtort_mbtest = 1; rcu_assign_pointer(rcu_torture_current, rp); smp_wmb(); /* Mods to old_rp must follow rcu_assign_pointer() */ From 269dcc1c2ec25864308ee03a3fa26ea819d9f5d0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 7 Sep 2010 14:23:09 -0700 Subject: [PATCH 46/52] rcu: Add tracing data to support queueing models The current tracing data is not sufficient to deduce the average time that a callback spends waiting for a grace period to end. Add three per-CPU counters recording the number of callbacks invoked (ci), the number of callbacks orphaned (co), and the number of callbacks adopted (ca). Given the existing callback queue length (ql), the average wait time in absence of CPU hotplug operations is ql/ci. The units of wait time will be in terms of the duration over which ci was measured. In the presence of CPU hotplug operations, there is room for argument, but ql/(ci-co+ca) won't steer you too far wrong. Also fixes a typo called out by Lucas De Marchi . Signed-off-by: Paul E. McKenney --- Documentation/RCU/trace.txt | 13 ++++++++++++- kernel/rcutree.c | 3 +++ kernel/rcutree.h | 3 +++ kernel/rcutree_trace.c | 10 +++++++--- 4 files changed, 25 insertions(+), 4 deletions(-) diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt index efd8cc95c06b..a851118775d8 100644 --- a/Documentation/RCU/trace.txt +++ b/Documentation/RCU/trace.txt @@ -125,6 +125,17 @@ o "b" is the batch limit for this CPU. If more than this number of RCU callbacks is ready to invoke, then the remainder will be deferred. +o "ci" is the number of RCU callbacks that have been invoked for + this CPU. Note that ci+ql is the number of callbacks that have + been registered in absence of CPU-hotplug activity. + +o "co" is the number of RCU callbacks that have been orphaned due to + this CPU going offline. + +o "ca" is the number of RCU callbacks that have been adopted due to + other CPUs going offline. Note that ci+co-ca+ql is the number of + RCU callbacks registered on this CPU. + There is also an rcu/rcudata.csv file with the same information in comma-separated-variable spreadsheet format. @@ -180,7 +191,7 @@ o "s" is the "signaled" state that drives force_quiescent_state()'s o "jfq" is the number of jiffies remaining for this grace period before force_quiescent_state() is invoked to help push things - along. Note that CPUs in dyntick-idle mode thoughout the grace + along. Note that CPUs in dyntick-idle mode throughout the grace period will not report on their own, but rather must be check by some other CPU via force_quiescent_state(). diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 42140a860bb9..e75073504a31 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1004,6 +1004,7 @@ static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp) for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; rsp->orphan_qlen += rdp->qlen; + rdp->n_cbs_orphaned += rdp->qlen; rdp->qlen = 0; raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ } @@ -1025,6 +1026,7 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_list; rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_tail; rdp->qlen += rsp->orphan_qlen; + rdp->n_cbs_adopted += rsp->orphan_qlen; rsp->orphan_cbs_list = NULL; rsp->orphan_cbs_tail = &rsp->orphan_cbs_list; rsp->orphan_qlen = 0; @@ -1156,6 +1158,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) /* Update count, and requeue any remaining callbacks. */ rdp->qlen -= count; + rdp->n_cbs_invoked += count; if (list != NULL) { *tail = rdp->nxtlist; rdp->nxtlist = list; diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 7918ba61873f..91d4170c5c13 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -202,6 +202,9 @@ struct rcu_data { long qlen; /* # of queued callbacks */ long qlen_last_fqs_check; /* qlen at last check for QS forcing */ + unsigned long n_cbs_invoked; /* count of RCU cbs invoked. */ + unsigned long n_cbs_orphaned; /* RCU cbs sent to orphanage. */ + unsigned long n_cbs_adopted; /* RCU cbs adopted from orphanage. */ unsigned long n_force_qs_snap; /* did other CPU force QS recently? */ long blimit; /* Upper limit on a processed batch */ diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index 458e032a3a30..d15430b9d122 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -64,7 +64,9 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp) rdp->dynticks_fqs); #endif /* #ifdef CONFIG_NO_HZ */ seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi); - seq_printf(m, " ql=%ld b=%ld\n", rdp->qlen, rdp->blimit); + seq_printf(m, " ql=%ld b=%ld", rdp->qlen, rdp->blimit); + seq_printf(m, " ci=%lu co=%lu ca=%lu\n", + rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted); } #define PRINT_RCU_DATA(name, func, m) \ @@ -119,7 +121,9 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp) rdp->dynticks_fqs); #endif /* #ifdef CONFIG_NO_HZ */ seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi); - seq_printf(m, ",%ld,%ld\n", rdp->qlen, rdp->blimit); + seq_printf(m, ",%ld,%ld", rdp->qlen, rdp->blimit); + seq_printf(m, ",%lu,%lu,%lu\n", + rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted); } static int show_rcudata_csv(struct seq_file *m, void *unused) @@ -128,7 +132,7 @@ static int show_rcudata_csv(struct seq_file *m, void *unused) #ifdef CONFIG_NO_HZ seq_puts(m, "\"dt\",\"dt nesting\",\"dn\",\"df\","); #endif /* #ifdef CONFIG_NO_HZ */ - seq_puts(m, "\"of\",\"ri\",\"ql\",\"b\"\n"); + seq_puts(m, "\"of\",\"ri\",\"ql\",\"b\",\"ci\",\"co\",\"ca\"\n"); #ifdef CONFIG_TREE_PREEMPT_RCU seq_puts(m, "\"rcu_preempt:\"\n"); PRINT_RCU_DATA(rcu_preempt_data, print_one_rcu_data_csv, m); From 2dfbf4dfbe47a484bae20456c12b40763b9b6af7 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 15 Sep 2010 23:30:48 -0700 Subject: [PATCH 47/52] rcu: Add advice to PROVE_RCU_REPEATEDLY kernel config parameter The PROVE_RCU_REPEATEDLY has no "Say Y"/"Say N" advice, so this commit adds it. Reported-by: Johannes Berg Signed-off-by: Paul E. McKenney --- lib/Kconfig.debug | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 52c2172dff16..9886cf5365ba 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -539,6 +539,10 @@ config PROVE_RCU_REPEATEDLY disabling, allowing multiple RCU-lockdep warnings to be printed on a single reboot. + Say Y to allow multiple RCU-lockdep warnings per boot. + + Say N if you are unsure. + config SPARSE_RCU_POINTER bool "RCU debugging: sparse-based checks for pointer usage" default n From 773e3f93577ffb493fb7c39b1a6ecf39b5748e87 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 5 Oct 2010 14:03:02 -0700 Subject: [PATCH 48/52] rcu: move check from rcu_dereference_bh to rcu_read_lock_bh_held As suggested by Linus, push the irqs_disabled() down to the rcu_read_lock_bh_held() level so that all callers get the benefit of the correct check. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 2 +- kernel/rcupdate.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 83af1f8d8b74..9fbc54a2585d 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -454,7 +454,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) * Makes rcu_dereference_check() do the dirty work. */ #define rcu_dereference_bh(p) \ - rcu_dereference_check(p, rcu_read_lock_bh_held() || irqs_disabled()) + rcu_dereference_check(p, rcu_read_lock_bh_held()) /** * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 4d169835fb36..0af1dc70fece 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -86,7 +86,7 @@ int rcu_read_lock_bh_held(void) { if (!debug_lockdep_rcu_enabled()) return 1; - return in_softirq(); + return in_softirq() || irqs_disabled(); } EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); From 1144182a8757f2a1f909f0c592898aaaf80884fc Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 6 Oct 2010 17:15:35 -0700 Subject: [PATCH 49/52] net: suppress RCU lockdep false positive in sock_update_classid > =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > include/linux/cgroup.h:542 invoked rcu_dereference_check() without protection! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 0 > 1 lock held by swapper/1: > #0: (net_mutex){+.+.+.}, at: [] > register_pernet_subsys+0x1f/0x47 > > stack backtrace: > Pid: 1, comm: swapper Not tainted 2.6.35.4-28.fc14.x86_64 #1 > Call Trace: > [] lockdep_rcu_dereference+0xaa/0xb3 > [] sock_update_classid+0x7c/0xa2 > [] sk_alloc+0x6b/0x77 > [] __netlink_create+0x37/0xab > [] ? rtnetlink_rcv+0x0/0x2d > [] netlink_kernel_create+0x74/0x19d > [] ? __mutex_lock_common+0x339/0x35b > [] rtnetlink_net_init+0x2e/0x48 > [] ops_init+0xe9/0xff > [] register_pernet_operations+0xab/0x130 > [] register_pernet_subsys+0x2e/0x47 > [] rtnetlink_init+0x53/0x102 > [] netlink_proto_init+0x126/0x143 > [] ? netlink_proto_init+0x0/0x143 > [] do_one_initcall+0x72/0x186 > [] kernel_init+0x23b/0x2c9 > [] kernel_thread_helper+0x4/0x10 > [] ? restore_args+0x0/0x30 > [] ? kernel_init+0x0/0x2c9 > [] ? kernel_thread_helper+0x0/0x10 The sock_update_classid() function calls task_cls_classid(current), but the calling task cannot go away, so there is no danger of the associated structures disappearing. Insert an RCU read-side critical section to suppress the false positive. Reported-by: Subrata Modak Signed-off-by: Paul E. McKenney --- net/core/sock.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/core/sock.c b/net/core/sock.c index ef30e9d286e7..7d99e13148e6 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1078,8 +1078,11 @@ static void sk_prot_free(struct proto *prot, struct sock *sk) #ifdef CONFIG_CGROUPS void sock_update_classid(struct sock *sk) { - u32 classid = task_cls_classid(current); + u32 classid; + rcu_read_lock(); /* doing current task, which cannot vanish. */ + classid = task_cls_classid(current); + rcu_read_unlock(); if (classid && classid != sk->sk_classid) sk->sk_classid = classid; } From b0a0f667a349247bd7f05f806b662a25653822bc Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 6 Oct 2010 17:32:51 -0700 Subject: [PATCH 50/52] sched: suppress RCU lockdep splat in task_fork_fair > =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > /home/greearb/git/linux.wireless-testing/kernel/sched.c:618 invoked rcu_dereference_check() without protection! > > other info that might help us debug this: > > rcu_scheduler_active = 1, debug_locks = 1 > 1 lock held by ifup/23517: > #0: (&rq->lock){-.-.-.}, at: [] task_fork_fair+0x3b/0x108 > > stack backtrace: > Pid: 23517, comm: ifup Not tainted 2.6.36-rc6-wl+ #5 > Call Trace: > [] ? printk+0xf/0x16 > [] lockdep_rcu_dereference+0x74/0x7d > [] task_group+0x6d/0x79 > [] set_task_rq+0xe/0x57 > [] task_fork_fair+0x57/0x108 > [] sched_fork+0x82/0xf9 > [] copy_process+0x569/0xe8e > [] do_fork+0x118/0x262 > [] ? do_page_fault+0x16a/0x2cf > [] ? up_read+0x16/0x2a > [] sys_clone+0x1b/0x20 > [] ptregs_clone+0x15/0x30 > [] ? sysenter_do_call+0x12/0x38 Here a newly created task is having its runqueue assigned. The new task is not yet on the tasklist, so cannot go away. This is therefore a false positive, suppress with an RCU read-side critical section. Reported-by: Ben Greear Tested-by: Ben Greear Date: Tue, 28 Sep 2010 16:32:43 +0800 Subject: [PATCH 51/52] rcu: using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value Using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value due to the caller didn't hold the root_rcu/rnp node's lock. Although use without ACCESS_ONCE() is safe due to the value loaded being used but once, the ACCESS_ONCE() is a good documentation aid -- the variables are being loaded without the services of a lock. Signed-off-by: Dongdong Deng CC: Dipankar Sarma CC: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e75073504a31..ccdc04c47981 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -545,9 +545,9 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) if (rcu_cpu_stall_suppress) return; - delta = jiffies - rsp->jiffies_stall; + delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall); rnp = rdp->mynode; - if ((rnp->qsmask & rdp->grpmask) && delta >= 0) { + if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) { /* We haven't checked in, so go dump stack. */ print_cpu_stall(rsp); From 6506cf6ce68d78a5470a8360c965dafe8e4b78e3 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 16 Sep 2010 17:50:31 +0200 Subject: [PATCH 52/52] sched: fix RCU lockdep splat from task_group() This addresses the following RCU lockdep splat: [0.051203] CPU0: AMD QEMU Virtual CPU version 0.12.4 stepping 03 [0.052999] lockdep: fixing up alternatives. [0.054105] [0.054106] =================================================== [0.054999] [ INFO: suspicious rcu_dereference_check() usage. ] [0.054999] --------------------------------------------------- [0.054999] kernel/sched.c:616 invoked rcu_dereference_check() without protection! [0.054999] [0.054999] other info that might help us debug this: [0.054999] [0.054999] [0.054999] rcu_scheduler_active = 1, debug_locks = 1 [0.054999] 3 locks held by swapper/1: [0.054999] #0: (cpu_add_remove_lock){+.+.+.}, at: [] cpu_up+0x42/0x6a [0.054999] #1: (cpu_hotplug.lock){+.+.+.}, at: [] cpu_hotplug_begin+0x2a/0x51 [0.054999] #2: (&rq->lock){-.-...}, at: [] init_idle+0x2f/0x113 [0.054999] [0.054999] stack backtrace: [0.054999] Pid: 1, comm: swapper Not tainted 2.6.35 #1 [0.054999] Call Trace: [0.054999] [] lockdep_rcu_dereference+0x9b/0xa3 [0.054999] [] task_group+0x7b/0x8a [0.054999] [] set_task_rq+0x13/0x40 [0.054999] [] init_idle+0xd2/0x113 [0.054999] [] fork_idle+0xb8/0xc7 [0.054999] [] ? mark_held_locks+0x4d/0x6b [0.054999] [] do_fork_idle+0x17/0x2b [0.054999] [] native_cpu_up+0x1c1/0x724 [0.054999] [] ? do_fork_idle+0x0/0x2b [0.054999] [] _cpu_up+0xac/0x127 [0.054999] [] cpu_up+0x55/0x6a [0.054999] [] kernel_init+0xe1/0x1ff [0.054999] [] kernel_thread_helper+0x4/0x10 [0.054999] [] ? restore_args+0x0/0x30 [0.054999] [] ? kernel_init+0x0/0x1ff [0.054999] [] ? kernel_thread_helper+0x0/0x10 [0.056074] Booting Node 0, Processors #1lockdep: fixing up alternatives. [0.130045] #2lockdep: fixing up alternatives. [0.203089] #3 Ok. [0.275286] Brought up 4 CPUs [0.276005] Total of 4 processors activated (16017.17 BogoMIPS). The cgroup_subsys_state structures referenced by idle tasks are never freed, because the idle tasks should be part of the root cgroup, which is not removable. The problem is that while we do in-fact hold rq->lock, the newly spawned idle thread's cpu is not yet set to the correct cpu so the lockdep check in task_group(): lockdep_is_held(&task_rq(p)->lock) will fail. But this is a chicken and egg problem. Setting the CPU's runqueue requires that the CPU's runqueue already be set. ;-) So insert an RCU read-side critical section to avoid the complaint. Signed-off-by: Peter Zijlstra Signed-off-by: Paul E. McKenney --- kernel/sched.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/sched.c b/kernel/sched.c index dc85ceb90832..ae8f75a5ceb4 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -5337,7 +5337,19 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu) idle->se.exec_start = sched_clock(); cpumask_copy(&idle->cpus_allowed, cpumask_of(cpu)); + /* + * We're having a chicken and egg problem, even though we are + * holding rq->lock, the cpu isn't yet set to this cpu so the + * lockdep check in task_group() will fail. + * + * Similar case to sched_fork(). / Alternatively we could + * use task_rq_lock() here and obtain the other rq->lock. + * + * Silence PROVE_RCU + */ + rcu_read_lock(); __set_task_cpu(idle, cpu); + rcu_read_unlock(); rq->curr = rq->idle = idle; #if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW)