linux-kernel - Re: [PATCH 5/5] coredump: ignore non-fatal signals when core dumping to a pipe

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Date:	Tue, 19 Feb 2013 20:45:17 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Mandeep Singh Baines <msb@...omium.org>
Cc:	linux-kernel@...r.kernel.org, Ben Chan <benchan@...omium.org>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 5/5] coredump: ignore non-fatal signals when core
	dumping to a pipe

On 02/19, Mandeep Singh Baines wrote:
>
> On Tue, Feb 19, 2013 at 6:27 AM, Oleg Nesterov <oleg@...hat.com> 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.

Great!

> >> 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 ;)

Oleg.

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