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    Subject[PATCH 3/3] sched: fix cgroup movement of waking process
    There is a small race between try_to_wake_up() and sched_move_task(), which is trying
    to move the process being woken up.

    try_to_wake_up() on CPU0 sched_move_task() on CPU1
    --------------------------------+---------------------------------
    raw_spin_lock_irqsave(p->pi_lock)
    task_waking_fair()
    ->p.se.vruntime -= cfs_rq->min_vruntime
    ttwu_queue()
    ->send reschedule IPI to another CPU1
    raw_spin_unlock_irqsave(p->pi_lock)
    task_rq_lock()
    -> tring to aquire both p->pi_lock and rq->lock
    with IRQ disabled
    task_move_group_fair()
    ->p.se.vruntime -= (old)cfs_rq->min_vruntime
    ->p.se.vruntime += (new)cfs_rq->min_vruntime
    task_rq_unlock()

    (via IPI)
    sched_ttwu_pending()
    raw_spin_lock(rq->lock)
    ttwu_do_activate()
    ...
    enqueue_entity()
    child.se->vruntime += cfs_rq->min_vruntime
    raw_spin_unlock(rq->lock)

    As a result, vruntime of the process becomes far bigger than min_vruntime,
    if (new)cfs_rq->min_vruntime >> (old)cfs_rq->min_vruntime.

    This patch fixes this problem by just ignoring such process in task_move_group_fair(),
    because the vruntime has already been normalized in task_waking_fair().

    Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    ---
    kernel/sched_fair.c | 4 ++--
    1 files changed, 2 insertions(+), 2 deletions(-)

    diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
    index bdaa4ab..3feb3a2 100644
    --- a/kernel/sched_fair.c
    +++ b/kernel/sched_fair.c
    @@ -4925,10 +4925,10 @@ static void task_move_group_fair(struct task_struct *p, int on_rq)
    * to another cgroup's rq. This does somewhat interfere with the
    * fair sleeper stuff for the first placement, but who cares.
    */
    - if (!on_rq && p->state != TASK_RUNNING)
    + if (!on_rq && p->state != TASK_RUNNING && p->state != TASK_WAKING)
    p->se.vruntime -= cfs_rq_of(&p->se)->min_vruntime;
    set_task_rq(p, task_cpu(p));
    - if (!on_rq && p->state != TASK_RUNNING)
    + if (!on_rq && p->state != TASK_RUNNING && p->state != TASK_WAKING)
    p->se.vruntime += cfs_rq_of(&p->se)->min_vruntime;
    }
    #endif
    --
    1.7.1


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