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 15:18:39 +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 02/18, Mandeep Singh Baines wrote:
>
> On Sat, Feb 16, 2013 at 11:46 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >>
> >> Why? __fatal_signal_pending() is enough, you do not need to check
> >> ->shared_pending. And once again, ignoring the freezer problems I
> >> do not think we need this check at all.
> >>
>
> The problem is that the kill signal remains in shared pending since
> it'll never get dequeued.
>
> localhost ~ # kill -KILL $!
> localhost ~ # cat /proc/$!/status | grep -A4 SigPnd
> SigPnd: 0000000000000000
> ShdPnd: 0000000000000100
> SigBlk: 0000000000000000
> SigIgn: 0000000000000000
> SigCgt: 0000000000000000
>
> Normally a fatal signal will get propagated to the whole group but
> that doesn't happen here because GROUP_EXIT is set:

Exactly!

>From the changelog in
"[PATCH 2/3] coredump: ensure that SIGKILL always kills the dumping thread"

	even if the dumping process is single-threaded
	...
	the group-wide SIGKILL is not recorded in task->pending
	and thus __fatal_signal_pending() won't be true.

Another reason why I think we should fix the underlying problem(s)
instead of adding more hacks,

> What if complete_signal was changed to propagate KILL even if
> SIGNAL_GROUP_EXIT is set?

See above, I think we can do better. And once again, 1/3 alone should
fix this problem with the non-fatal signals.

Oleg.

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