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    SubjectRe: [PATCH 09/11] job control: reorganize wait_task_stopped()
    Hi,

    On 05/13, Tejun Heo wrote:
    >
    > On Thu, May 12, 2011 at 08:33:26PM +0200, Oleg Nesterov wrote:
    >
    > > At first glance, do_wait() does
    > >
    > > wait_task_stopped();
    > > wait_task_continued();
    > >
    > > and the state can be changed CONTINIUED -> STOPPED in between, right?
    > > Or something else?
    >
    > Yeah and exit transitions too.

    I am not sure... but probably this depends on definition.

    We already checked ->exit_state != ZOMBIE, and we are holding tasklist.
    The child can't exit. I mean, it can't change its ->exit_state.

    However, SIGKILL can clear SIGNAL_STOP_STOPPED, and we can "miss" it.
    But this looks correct, the child is no longer stopped but it is still
    not dead. So I think in this case wait(WNOHANG | WEXITED | WSTOPPED)
    can fail, notabug.

    OTOH, perhaps SIGKILL should set SIGNAL_STOP_CONTINUED in this case?
    And keep it if it was already set.

    > There simply is no synchronization
    > there. We can probably solve it without acquiring siglock by adding
    > "clear this before making state transitions" flag followed by a mb()

    perhaps even simpler if ->EXIT transition is fine.

    Oleg.



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