linux-kernel - Re: [PATCH] coredump: Retry writes where appropriate

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Date:	Mon, 1 Jun 2009 18:12:34 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	paul@...-scientist.net, linux-kernel@...r.kernel.org,
	stable@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [PATCH] coredump: Retry writes where appropriate

On 05/31, Alan Cox wrote:
>
> On Sun, 31 May 2009 01:33:39 -0400
> Paul Smith <paul@...-scientist.net> wrote:
>
> > coredump: Retry writes where appropriate
> >
> > Core dump write operations (especially to a pipe) can be incomplete due
> > to signal reception or possibly recoverable partial writes.
>
> NAK this
>
> > Previously any incomplete write in the ELF core dumper caused the core
> > dump to stop, giving short cores in these cases.  Modify the core dumper
> > to retry the write where appropriate.
>
> The existing behaviour is an absolute godsend when you've something like
> a core dump stuck on an NFS mount or something trying to core dump to
> very slow media.

I agree, we should make the coredumping interruptible.

But I don't know which signal should intterrupt. At least SIGKILL should,
I think. As for other unhandled sig_fatal() signals, I am nor sure.
I can make a patch, but first I need to know what this patch should do.
Again, please look at:

	killable/interruptible coredumps
	http://marc.info/?l=linux-kernel&m=121665710711931


And we should not change dump_write(), we should create the new helper
which can be used by all fs/binfmt_*.c.

And of course, the coredumping thread should not play with ->blocked
or ->sighand->action. This is not even needed.

Oleg.

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