linux-kernel - Re: [PATCH 5/5] coredump: abort core dump piping only due to a fatal signal

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Date:	Fri, 15 Feb 2013 16:01:17 +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: abort core dump piping only due to a
	fatal signal

On 02/14, Mandeep Singh Baines wrote:
>
> This patch makes wait_for_dump_helpers() not to abort piping the core
> dump data when the crashing process has received any but a fatal signal
> (SIGKILL). The rationale is that a crashing process may still receive
> uninteresting signals such as SIGCHLD when its core dump data is being
> redirected to a helper application.

You already sent this change in the past ;) and I already reviewed it.

It is not enough and imho not good. Damn, I'll try very much to make the
patches on weekend...

> -	while ((pipe->readers > 1) && (!signal_pending(current))) {
> +	while ((pipe->readers > 1) && (!fatal_signal_pending(current))) {

This turns pipe_wait() belowe into the busy-wait loop if signal_pending().
Not good. And not enough, there are other reasons why coredump can fail
if the signal is pending.

>  		wake_up_interruptible_sync(&pipe->wait);
>  		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
>  		pipe_wait(pipe);
> +		pipe_unlock(pipe);
> +		try_to_freeze();

Oh, yes. One of the problems with coredump/signals is freezer. Not sure
what should we do...

But if we add try_to_freeze() here, we need to add more try_to_freeze's,
think about dumping the huge core on the slow media.

Oleg.

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