Commit-ID: a18b5d01819235629289212ad428a5ee2b40f0d9
Gitweb: http://git.kernel.org/tip/a18b5d01819235629289212ad428a5ee2b40f0d9
Author: Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Thu, 22 Jan 2015 18:08:04 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 30 Jan 2015 19:38:51 +0100
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@xxxxxxxxxxxxxxxxxxxx>
Reported-by: Ingo Molnar <mingo@xxxxxxxxxx>
Original-patch-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1421946484-9298-1-git-send-email-fweisbec@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/core.c | 40 +++++++++++++++++++---------------------
1 file changed, 19 insertions(+), 21 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0b591fe..54dce01 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;
}
--
To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
|