[tip:sched/urgent] sched, kvm: Fix race condition involving sched_in_preempt_notifers

[tip-bot for Tejun Heo]

Commit-ID:  498657a478c60be092208422fefa9c7b248729c2
Gitweb:     http://git.kernel.org/tip/498657a478c60be092208422fefa9c7b248729c2
Author:     Tejun Heo <tj@xxxxxxxxxx>
AuthorDate: Fri, 13 Nov 2009 18:33:53 +0900
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Sun, 15 Nov 2009 09:59:54 +0100

sched, kvm: Fix race condition involving sched_in_preempt_notifers

In finish_task_switch(), fire_sched_in_preempt_notifiers() is
called after finish_lock_switch().

However, depending on architecture, preemption can be enabled after
finish_lock_switch() which breaks the semantics of preempt
notifiers.

So move it before finish_arch_switch(). This also makes the in-
notifiers symmetric to out- notifiers in terms of locking - now
both are called under rq lock.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Avi Kivity <avi@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <4AFD2801.7020900@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/sched.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 701eca4..cea2bea 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2758,9 +2758,9 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
 	prev_state = prev->state;
 	finish_arch_switch(prev);
 	perf_event_task_sched_in(current, cpu_of(rq));
+	fire_sched_in_preempt_notifiers(current);
 	finish_lock_switch(rq, prev);
 
-	fire_sched_in_preempt_notifiers(current);
 	if (mm)
 		mmdrop(mm);
 	if (unlikely(prev_state == TASK_DEAD)) {
--
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