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rcu: Make ksoftirqd do RCU quiescent states 

Implementing RCU-bh in terms of RCU-preempt makes the system vulnerable
to network-based denial-of-service attacks.  This patch therefore
makes __do_softirq() invoke rcu_bh_qs(), but only when __do_softirq()
is running in ksoftirqd context.  A wrapper layer in interposed so that
other calls to __do_softirq() avoid invoking rcu_bh_qs().  The underlying
function __do_softirq_common() does the actual work.

The reason that rcu_bh_qs() is bad in these non-ksoftirqd contexts is
that there might be a local_bh_enable() inside an RCU-preempt read-side
critical section.  This local_bh_enable() can invoke __do_softirq()
directly, so if __do_softirq() were to invoke rcu_bh_qs() (which just
calls rcu_preempt_qs() in the PREEMPT_RT_FULL case), there would be
an illegal RCU-preempt quiescent state in the middle of an RCU-preempt
read-side critical section.  Therefore, quiescent states can only happen
in cases where __do_softirq() is invoked directly from ksoftirqd.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20111005184518.GA21601@linux.vnet.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Paul E. McKenney 2011-10-05 11:45:18 -07:00 committed by Alibek Omarov
parent 482b29e64e
commit 010ec70629
4 changed files with 27 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/rcupdate.h
View File

@ -229,13 +229,7 @@ static inline int rcu_preempt_depth(void)
/* Internal to kernel */
void rcu_init(void);
void rcu_sched_qs(int cpu);
#ifdef CONFIG_PREEMPT_RT_FULL
static inline void rcu_bh_qs(int cpu) { }
#else
void rcu_bh_qs(int cpu);
#endif
void rcu_check_callbacks(int cpu, int user);
struct notifier_block;
void rcu_idle_enter(void);

9
kernel/rcu/tree.c
View File

@ -199,7 +199,14 @@ void rcu_sched_qs(int cpu)
rdp->passed_quiesce = 1;
}
#ifndef CONFIG_PREEMPT_RT_FULL
#ifdef CONFIG_PREEMPT_RT_FULL
static void rcu_preempt_qs(int cpu);
void rcu_bh_qs(int cpu)
{
rcu_preempt_qs(cpu);
}
#else
void rcu_bh_qs(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);

8
kernel/rcu/tree_plugin.h
View File

@ -1575,7 +1575,7 @@ static void rcu_prepare_kthreads(int cpu)
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#if !defined(CONFIG_RCU_FAST_NO_HZ)
#if !defined(CONFIG_RCU_FAST_NO_HZ) || defined(CONFIG_PREEMPT_RT_FULL)
/*
* Check to see if any future RCU-related work will need to be done
@ -1591,6 +1591,9 @@ int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
*delta_jiffies = ULONG_MAX;
return rcu_cpu_has_callbacks(cpu, NULL);
}
#endif /* !defined(CONFIG_RCU_FAST_NO_HZ) || defined(CONFIG_PREEMPT_RT_FULL) */
#if !defined(CONFIG_RCU_FAST_NO_HZ)
/*
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
@ -1688,6 +1691,8 @@ static bool rcu_try_advance_all_cbs(void)
return cbs_ready;
}
#ifndef CONFIG_PREEMPT_RT_FULL
/*
* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
* to invoke. If the CPU has callbacks, try to advance them. Tell the
@ -1726,6 +1731,7 @@ int rcu_needs_cpu(int cpu, unsigned long *dj)
}
return 0;
}
#endif /* #ifndef CONFIG_PREEMPT_RT_FULL */
/*
* Prepare a CPU for idle from an RCU perspective. The first major task

18
kernel/softirq.c
View File

@ -141,7 +141,7 @@ static void wakeup_softirqd(void)
wake_up_process(tsk);
}
static void handle_pending_softirqs(u32 pending, int cpu)
static void handle_pending_softirqs(u32 pending, int cpu, int need_rcu_bh_qs)
{
struct softirq_action *h = softirq_vec;
unsigned int prev_count = preempt_count();
@ -167,7 +167,8 @@ static void handle_pending_softirqs(u32 pending, int cpu)
prev_count, preempt_count());
preempt_count_set(prev_count);
}
rcu_bh_qs(cpu);
if (need_rcu_bh_qs)
rcu_bh_qs(cpu);
h++;
pending >>= softirq_bit;
}
@ -349,7 +350,7 @@ restart:
/* Reset the pending bitmask before enabling irqs */
set_softirq_pending(0);
handle_pending_softirqs(pending, cpu);
handle_pending_softirqs(pending, cpu, 1);
pending = local_softirq_pending();
if (pending) {
@ -398,7 +399,12 @@ static void ksoftirqd_clr_sched_params(unsigned int cpu, bool online) { }
static DEFINE_LOCAL_IRQ_LOCK(local_softirq_lock);
static DEFINE_PER_CPU(struct task_struct *, local_softirq_runner);
asmlinkage void __do_softirq(void);
static void __do_softirq_common(int need_rcu_bh_qs);
asmlinkage __do_softirq(void)
{
__do_softirq_common(0);
}
void __init softirq_early_init(void)
{
@ -507,7 +513,7 @@ asmlinkage void __do_softirq(void)
lockdep_softirq_enter();
handle_pending_softirqs(pending, cpu);
handle_pending_softirqs(pending, cpu, need_rcu_bh_qs);
pending = local_softirq_pending();
if (pending)
@ -546,7 +552,7 @@ static int __thread_do_softirq(int cpu)
* schedule!
*/
if (local_softirq_pending())
__do_softirq();
__do_softirq_common(cpu >= 0);
local_unlock(local_softirq_lock);
unpin_current_cpu();
preempt_disable();