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| author | Frederic Weisbecker <fweisbec@gmail.com> | 2015-01-22 18:08:04 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-01-30 19:38:51 +0100 |
| commit | a18b5d01819235629289212ad428a5ee2b40f0d9 (patch) | |
| tree | 9e3b0c3fdf4f9e994b13ee200cf32f5b2a311e88 /kernel | |
| parent | 80e3d87b2c5582db0ab5e39610ce3707d97ba409 (diff) | |
| download | linux-a18b5d01819235629289212ad428a5ee2b40f0d9.tar.bz2 | |
sched: Fix missing preemption opportunity
If an interrupt fires in cond_resched(), between the call to __schedule()
and the PREEMPT_ACTIVE count decrementation, and that interrupt sets
TIF_NEED_RESCHED, the call to preempt_schedule_irq() will be ignored
due to the PREEMPT_ACTIVE count. This kind of scenario, with irq preemption
being delayed because it's interrupting a preempt-disabled area, is
usually fixed up after preemption is re-enabled back with an explicit
call to preempt_schedule().
This is what preempt_enable() does but a raw preempt count decrement as
performed by __preempt_count_sub(PREEMPT_ACTIVE) doesn't handle delayed
preemption check. Therefore when such a race happens, the rescheduling
is going to be delayed until the next scheduler or preemption entrypoint.
This can be a problem for scheduler latency sensitive workloads.
Lets fix that by consolidating cond_resched() with preempt_schedule()
internals.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Ingo Molnar <mingo@kernel.org>
Original-patch-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1421946484-9298-1-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/core.c | 40 |
1 files changed, 19 insertions, 21 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0b591fe67b70..54dce019c0ce 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2884,6 +2884,21 @@ void __sched schedule_preempt_disabled(void) preempt_disable(); } +static void preempt_schedule_common(void) +{ + do { + __preempt_count_add(PREEMPT_ACTIVE); + __schedule(); + __preempt_count_sub(PREEMPT_ACTIVE); + + /* + * Check again in case we missed a preemption opportunity + * between schedule and now. + */ + barrier(); + } while (need_resched()); +} + #ifdef CONFIG_PREEMPT /* * this is the entry point to schedule() from in-kernel preemption @@ -2899,17 +2914,7 @@ asmlinkage __visible void __sched notrace preempt_schedule(void) if (likely(!preemptible())) return; - do { - __preempt_count_add(PREEMPT_ACTIVE); - __schedule(); - __preempt_count_sub(PREEMPT_ACTIVE); - - /* - * Check again in case we missed a preemption opportunity - * between schedule and now. - */ - barrier(); - } while (need_resched()); + preempt_schedule_common(); } NOKPROBE_SYMBOL(preempt_schedule); EXPORT_SYMBOL(preempt_schedule); @@ -4209,17 +4214,10 @@ SYSCALL_DEFINE0(sched_yield) return 0; } -static void __cond_resched(void) -{ - __preempt_count_add(PREEMPT_ACTIVE); - __schedule(); - __preempt_count_sub(PREEMPT_ACTIVE); -} - int __sched _cond_resched(void) { if (should_resched()) { - __cond_resched(); + preempt_schedule_common(); return 1; } return 0; @@ -4244,7 +4242,7 @@ int __cond_resched_lock(spinlock_t *lock) if (spin_needbreak(lock) || resched) { spin_unlock(lock); if (resched) - __cond_resched(); + preempt_schedule_common(); else cpu_relax(); ret = 1; @@ -4260,7 +4258,7 @@ int __sched __cond_resched_softirq(void) if (should_resched()) { local_bh_enable(); - __cond_resched(); + preempt_schedule_common(); local_bh_disable(); return 1; } |