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@kernel.org>
Acked-by: Avi Kivity <avi@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4AFD2801.7020900@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 701eca4958a23af6ca0796e7493347baa773a4aa..cea2beac79096047400ad2c54e48ec660f1c0270 100644 (file)
--- 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)) {