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    Subject[tip:sched/core] sched: Fix cgroup movement of waking process
    Commit-ID:  62af3783e4fd8ba9e28416e8e91cb3bdd9fb133e
    Gitweb: http://git.kernel.org/tip/62af3783e4fd8ba9e28416e8e91cb3bdd9fb133e
    Author: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    AuthorDate: Thu, 15 Dec 2011 14:37:41 +0900
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Wed, 21 Dec 2011 10:34:52 +0100

    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 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
    += (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>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Tejun Heo <tj@kernel.org>
    Link: http://lkml.kernel.org/r/20111215143741.df82dd50.nishimura@mxp.nes.nec.co.jp
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    kernel/sched/fair.c | 4 +++-
    1 files changed, 3 insertions(+), 1 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 2d1ac6e..bdf1883 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -5344,11 +5344,13 @@ static void task_move_group_fair(struct task_struct *p, int on_rq)
    *
    * - Moving a forked child which is waiting for being woken up by
    * wake_up_new_task().
    + * - Moving a task which has been woken up by try_to_wake_up() and
    + * waiting for actually being woken up by sched_ttwu_pending().
    *
    * To prevent boost or penalty in the new cfs_rq caused by delta
    * min_vruntime between the two cfs_rqs, we skip vruntime adjustment.
    */
    - if (!on_rq && !p->se.sum_exec_runtime)
    + if (!on_rq && (!p->se.sum_exec_runtime || p->state == TASK_WAKING))
    on_rq = 1;

    if (!on_rq)

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