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    SubjectRe: [PATCH] fix send_sigqueue() vs thread exit race
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    On Mon, 2005-08-22 at 10:39 +0400, Oleg Nesterov wrote:
    > Thomas Gleixner wrote:
    > >
    > > @@ -1427,7 +1434,18 @@ send_group_sigqueue(int sig, struct sigq
    > > int ret = 0;
    > >
    > > BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
    > > - read_lock(&tasklist_lock);
    > > +retry:
    > > + if (unlikely(p->flags & PF_EXITING))
    > > + return -1;
    > > +
    >
    > I don't think this is correct. p == ->group_leader, it may
    > have been exited and in EXIT_ZOMBIE state. But the thread
    > group (process) is live, we should not stop posix timers.

    Hmm, true. release_task() is not called in this case, so p->sighand is
    still there.

    But we can not check for p->sighand == NULL, as sighand is released
    after exit_itimers() so we are still deadlock prone. So I think
    __exit_sighand() should be called before exit_itimers(). Then we can do

    retry:
    if (unlikely(!p->sighand))
    return -1;

    instead of checking for PF_EXITING.

    tglx









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