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    SubjectRe: Q: cgroup: Questions about possible issues in cgroup locking
    On 12/21, Frederic Weisbecker wrote:
    >
    > On Wed, Dec 21, 2011 at 02:08:48PM +0100, Oleg Nesterov wrote:
    > > On 12/21, Frederic Weisbecker wrote:
    > > > - By the time we call cgroup_post_fork(), it is ready to be woken up
    > > > and usable by the scheduler.
    > >
    > > No, the new child can't run until do_fork()->wake_up_new_task().
    >
    > Out of curiosity, why is it not possible for a task to kill and wake up the child
    > before that happens?

    Because it is not possible to wake it up.

    Please note that copy_process() creates the "deactivated" child, iow
    it is not on rq.

    But, at the same time its ->state == TASK_RUNNING. This "fools"
    try_to_wake_up() or anything else which in theory could place it
    on the runqueue.

    Except, of course, wake_up_new_task() does activate_task(). And
    note that it does this unconditionally, exactly because we know that
    this task can't be woken.

    Oleg.



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