On Tue, 2005-08-23 at 20:17 +0400, Oleg Nesterov wrote:
> Thomas Gleixner wrote:
> > I still think the last patch I sent is still necessary.
>
> Thomas, you know that I like this change in __exit_{signal,sighand},
> but i think this change is dangerous, should go in a separate patch,
> and needs a
Thomas Gleixner wrote:
>
> On Mon, 2005-08-22 at 20:45 +0400, Oleg Nesterov wrote:
> >
> > kernel/posix-timers.c:common_timer_del() calls del_timer_sync(), after
> > that nobody can access this timer, so we don't need to lock timer->it_lock
> > at all in this case. No lock - no deadlock.
>
> It sti
On Mon, 2005-08-22 at 20:45 +0400, Oleg Nesterov wrote:
> But I know nothing about kernel/posix-cpu-timers.c, I doubt it will work
> for posix_cpu_timer_del(). I don't have time to study posix-cpu-timers now.
> However, I see that __exit_signal() calls posix_cpu_timers_exit_xxx(), so
> may be it ca
On Mon, 2005-08-22 at 20:45 +0400, Oleg Nesterov wrote:
> Thomas Gleixner wrote:
> Ok, exit_itimers()->itimer_delete() called when the last thread exits
> or does exec.
>
> kernel/posix-timers.c:common_timer_del() calls del_timer_sync(), after
> that nobody can access this timer, so we don't need
Thomas Gleixner wrote:
>
> 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))
>
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
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:
> > +
Oleg,
On Mon, 2005-08-22 at 12:52 +0400, Oleg Nesterov wrote:
> Thomas Gleixner wrote:
> I think yes, and this is closely related to your and Paul
> "Use RCU to protect tasklist for unicast signals" patches.
>
> We don't need RCU here, but we do need this hypothetical
> lock_task_sighand() (and _
Thomas Gleixner wrote:
>
> It exists. It triggers on preempt-RT and I can trigger it on vanilla SMP
> by waiting for the timer expiry in release_task() before the
> __exit_signal() call. That's reasonable, as it can happen that way by
> chance too. It requires that the timer expires on a different
On Sun, 2005-08-21 at 23:24 +0200, Thomas Gleixner wrote:
> Oleg,
Sorry for making noise. I introduced the race again.
tglx
--- linux-2.6.13-rc6.signal/kernel/signal.oleg.c2005-08-21
23:07:03.0 +0200
+++ linux-2.6.13-rc6.signal/kernel/signal.c 2005-08-21 23:48:52.0
Oleg,
On Sun, 2005-08-21 at 14:59 +0400, Oleg Nesterov wrote:
> CPU_0 CPU_1
>
> release_task: posix_timer_fn:
> write_lock(tasklist); lock(timer->it_lock);
>
> exit_timers:send_sigxx
On Sun, 2005-08-21 at 14:41 +0400, Oleg Nesterov wrote:
> If not:
>
> > timer event
> > timr->it_process references a freed structure
> >
>
> No, create_timer() does get_task_struct(timr->it_process), this
> task may be EXIT_DEAD now, but the task_struct itself is valid,
> and it's ->fl
Thomas Gleixner wrote:
>
> On Sat, 2005-08-20 at 20:58 +0400, Oleg Nesterov wrote:
> > [PATCH] fix send_sigqueue() vs thread exit race
> >
> > .
> > - read_lock(&tasklist_lock);
> > + read_lock(&tasklist_lock);
> > +
> > + if (unlikely(p->flags & PF_EXITING)) {
> > + re
On Sat, 2005-08-20 at 20:58 +0400, Oleg Nesterov wrote:
> [PATCH] fix send_sigqueue() vs thread exit race
>
> posix_timer_event() first checks that the thread (SIGEV_THREAD_ID
> case) does not have PF_EXITING flag, then it calls send_sigqueue()
> which locks task list. But if the thread exits in b
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