From 74de6960c99d8df0d09fb29a7b014cb9c5571e2b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 24 Jul 2018 15:28:09 -0700 Subject: [PATCH] rcu: Provide functions for determining if call_rcu() has been invoked This commit adds rcu_head_init() and rcu_head_after_call_rcu() functions to help RCU users detect when another CPU has passed the specified rcu_head structure and function to call_rcu(). The rcu_head_init() should be invoked before making the structure visible to RCU readers, and then the rcu_head_after_call_rcu() may be invoked from within an RCU read-side critical section on an rcu_head structure that was obtained during a traversal of the data structure in question. The rcu_head_after_call_rcu() function will return true if the rcu_head structure has already been passed (with the specified function) to call_rcu(), otherwise it will return false. If rcu_head_init() has not been invoked on the rcu_head structure or if the rcu_head (AKA callback) has already been invoked, then rcu_head_after_call_rcu() will do WARN_ON_ONCE(). Reported-by: NeilBrown Signed-off-by: Paul E. McKenney [ paulmck: Apply neilb naming feedback. ] --- include/linux/rcupdate.h | 40 ++++++++++++++++++++++++++++++++++++++++ kernel/rcu/rcu.h | 5 ++++- 2 files changed, 44 insertions(+), 1 deletion(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index e4f821165d0b..4db8bcacc51a 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -857,6 +857,46 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ +/* Has the specified rcu_head structure been handed to call_rcu()? */ + +/* + * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() + * @rhp: The rcu_head structure to initialize. + * + * If you intend to invoke rcu_head_after_call_rcu() to test whether a + * given rcu_head structure has already been passed to call_rcu(), then + * you must also invoke this rcu_head_init() function on it just after + * allocating that structure. Calls to this function must not race with + * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. + */ +static inline void rcu_head_init(struct rcu_head *rhp) +{ + rhp->func = (rcu_callback_t)~0L; +} + +/* + * rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()? + * @rhp: The rcu_head structure to test. + * @func: The function passed to call_rcu() along with @rhp. + * + * Returns @true if the @rhp has been passed to call_rcu() with @func, + * and @false otherwise. Emits a warning in any other case, including + * the case where @rhp has already been invoked after a grace period. + * Calls to this function must not race with callback invocation. One way + * to avoid such races is to enclose the call to rcu_head_after_call_rcu() + * in an RCU read-side critical section that includes a read-side fetch + * of the pointer to the structure containing @rhp. + */ +static inline bool +rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) +{ + if (READ_ONCE(rhp->func) == f) + return true; + WARN_ON_ONCE(READ_ONCE(rhp->func) != (rcu_callback_t)~0L); + return false; +} + + /* Transitional pre-consolidation compatibility definitions. */ static inline void synchronize_rcu_bh(void) diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 5dec94509a7e..4c56c1d98fb3 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -224,6 +224,7 @@ void kfree(const void *); */ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head) { + rcu_callback_t f; unsigned long offset = (unsigned long)head->func; rcu_lock_acquire(&rcu_callback_map); @@ -234,7 +235,9 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head) return true; } else { RCU_TRACE(trace_rcu_invoke_callback(rn, head);) - head->func(head); + f = head->func; + WRITE_ONCE(head->func, (rcu_callback_t)0L); + f(head); rcu_lock_release(&rcu_callback_map); return false; }