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    Subject[PATCH 1/3] sched: fix cgroup movement of newly created process
    There is a small race between do_fork() and sched_move_task(), which is trying
    to move the child.

    do_fork() sched_move_task()
    --------------------------------+---------------------------------
    copy_process()
    sched_fork()
    task_fork_fair()
    -> vruntime of the child is initialized
    based on that of the parent.
    -> we can see the child in "tasks" file now.
    task_rq_lock()
    task_move_group_fair()
    ->child.se.vruntime -= (old)cfs_rq->min_vruntime
    ->child.se.vruntime += (new)cfs_rq->min_vruntime
    task_rq_unlock()
    wake_up_new_task()
    ...
    enqueue_entity()
    child.se->vruntime += cfs_rq->min_vruntime

    As a result, vruntime of the child 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_fork_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 5c9e679..df145a9 100644
    --- a/kernel/sched_fair.c
    +++ b/kernel/sched_fair.c
    @@ -4922,10 +4922,10 @@ 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)
    + if (!on_rq && p->state != TASK_RUNNING)
    p->se.vruntime -= cfs_rq_of(&p->se)->min_vruntime;
    set_task_rq(p, task_cpu(p));
    - if (!on_rq)
    + if (!on_rq && p->state != TASK_RUNNING)
    p->se.vruntime += cfs_rq_of(&p->se)->min_vruntime;
    }
    #endif
    --
    1.7.1


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