linux-kernel - [PATCH 02/21] sched, kvm: fix race condition involving sched_in_preempt

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Message-Id: <1258391726-30264-3-git-send-email-tj@kernel.org>
Date:	Tue, 17 Nov 2009 02:15:07 +0900
From:	Tejun Heo <tj@...nel.org>
To:	linux-kernel@...r.kernel.org, jeff@...zik.org, mingo@...e.hu,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com,
	torvalds@...ux-foundation.org, avi@...hat.com,
	peterz@...radead.org, andi@...stfloor.org, fweisbec@...il.com
Cc:	Tejun Heo <tj@...nel.org>
Subject: [PATCH 02/21] 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.  Move it before finish_arch_switch().
This also makes in notifiers symmetric to out notifiers in terms of
locking - now both are called under rq lock.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Avi Kivity <avi@...hat.com>
---
 kernel/sched.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 3c11ae0..de8a765 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2751,9 +2751,9 @@ 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)) {
-- 
1.6.4.2

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