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 12:20:04 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
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 Tue, Feb 19, 2013 at 11:45 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> 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.
>

Ah. Good point. How about this then:

/* can't use wait_event_freezable since we suppress the fake signal on
SIGNAL_GROUP_COREDUMP */
freezer_do_not_count();
wait_event_interruptible(pipe->wait, pipe->readers == 1);
freezer_count();

Regards,
Mandeep

> 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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