Re: [PATCH 5/5] coredump: ignore non-fatal signals when coredumping to a pipe

From: Oleg Nesterov
Date: Tue Feb 19 2013 - 14:46:45 EST

On 02/19, Mandeep Singh Baines wrote:
> On Tue, Feb 19, 2013 at 6:27 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> > Please look at 1-3 I sent. Btw, I slightly tested this series, seems
> > to work...
> >
> They look good to me. I plan on applying them to our tree since we
> need a fix ASAP.


> >> You'd need to prevent the fake signal from freeezer from setting
> >> TIF_SIGPENDING. Maybe just add a SIGNAL_GROUP_EXIT check in freezer.c.
> >
> > I am thinking about checking SIGNAL_GROUP_COREDUMP but I am not sure,
> > perhaps we can make a simpler solution. As for wait_for_dump_helper()
> > we do not need any check at all, but we should either fix
> > wait_event_freezable (it is actually not right) or change pipe_release()
> Is the bug that it will exit on the fake_signal.

Yes, I understand, but

> I don't think that bug will affects this patch though. I think this
> should all work if we add a check to freezer.c (or something similar
> that is cleaner).
> If you add SIGNAL_GROUP_COREDUMP check to freezer.c:
> static void fake_signal_wake_up(struct task_struct *p)
> {
> unsigned long flags;
> if (lock_task_sighand(p, &flags)) {
> - signal_wake_up(p, 0);
> + if (!p->signal->flags & SIGNAL_GROUP_COREDUMP)
> + signal_wake_up(p, 0);
> unlock_task_sighand(p, &flags);
> }
> }
> And change the wait_event_freezekillable() in this patch to just
> wait_event_freezable(), shouldn't that just work.

I doubt,

> The fake signal will never get sent.

Yes but try_to_freeze_tasks() can fail.

And once again, if wait_event_freezable() was correct we do not care
about the fake signal (in wait_for_dump_helper), so we do not need
to change fake_signal_wake_up. So perhaps we should fix it but this
needs some discussion.

Sorry again for the terse reply (and perhaps I misunderstood you),
I'll try to return to this problem asap. In any case I still think
we should do the freezer fixes on top of signal fixes I sent, and
you seem to agree. Good ;)


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