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    SubjectRe: [PATCH 3/4] threadgroup: extend threadgroup_lock() to cover exit and exec
    On 09/18, Oleg Nesterov wrote:
    >
    > Of course I am in no position to ack the changes in this code, I do not
    > fell I understand it enough. But afaics this series is fine.
    ^^^^
    I do not feel ;)

    > If I am right, afaics the only change 4/4 needs is that it should not add
    > WARN_ON_ONCE(tsk->flags & PF_EXITING) into cgroup_task_migrate().

    Hmm. Unless I missed something this WARN_ON_ONCE() is not right anyway,
    because

    > - * Call holding cgroup_mutex. May take task_lock of
    > - * the task 'tsk' during call.
    > + * Call with cgroup_mutex and threadgroup locked. May take task_lock of
    > + * @tsk during call.
    > */
    > int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)

    this is not true, cgroup_attach_proc() has other callers.

    cgroup_attach_task_all() is probably fine, tsk should be current.

    but cpuset_do_move_task() doesn't look fine at first glance, we can race
    with the exiting task.

    And this leads to another question about the cgroup_mutex/threadgroup_lock
    nesting...

    Oleg.



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