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    Subject[PATCH 02/21] sched, kvm: fix race condition involving sched_in_preempt_notifers
    Date
    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@kernel.org>
    Cc: Avi Kivity <avi@redhat.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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