linux-kernel - Re: [PATCH 0/3] coredump: fix the ancient signal problems

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Date:	Sun, 17 Feb 2013 20:50:44 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...IV.linux.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...hat.com>,
	Mandeep Singh Baines <msb@...omium.org>,
	Neil Horman <nhorman@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Roland McGrath <roland@...k.frob.com>,
	Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] coredump: fix the ancient signal problems

On 02/17, Linus Torvalds wrote:
>
> On Sun, Feb 17, 2013 at 11:18 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > Linus, et al, could you please ack/nack the intent? Of course I will
> > appreciate if you can review the code, but what I am actually worried
> > about is the user-visible change: the coredumping becomes killable but
> > only by the _explicit_ SIGKILL, other fatal signals are "ignored".
>
> That isn't a problem. In fact, we already have logic that makes the
> act of writing a file be killable by SIGKILL (because you really
> really want that for network filesystems, for example), so I suspect
> that core-dumping was interruptible by SIGKILL even before you made it
> explicitly so - simply because the IO itself was.

Yes, and even pipe_write() can fail if signal_pending() == T.

> And even if it wasn't (because maybe the SIGKILL logic doesn't get
> triggered due to all the special-case core-dumping code in signal
> handling),

Yes, SIGKILL can wakeup (or can miss) the dumping thread sleeping in
->write() but this is not enough. See 2/3.

> SIGKILL really is very very special. Having it kill a
> coredump in progress sounds fine to me.

Great.

> That said, I'm not convinced about your particular split of patches.
> The first patch introduces that new SIGNAL_GROUP_COREDUMP, and then
> the second patch modifies one of the new use cases:
>
> -               tsk->signal->flags |= SIGNAL_GROUP_COREDUMP;
> +               tsk->signal->flags = SIGNAL_GROUP_COREDUMP;
>
>
> and that just smells to me like you tried too hard to split things
> into two patches.

Oh, I disagree, but I wouldn't mind to join these changes assuming
they pass the review (including my self-review tomorrow).

To me, the splitting is "natural". 1/3 protects the dumping thread
from !SIGKILL signals, 2/3 makes makes the dumping thread killable.

Another reason for 1/3 in a separate patch is the documentation,
I think we need more changes in prepare_signal(SIGNAL_GROUP_EXIT)
case.

But I won't insist.

> I wonder if Al
> Viro hould be on the cc.

Hello Al.

I'll send you mbox with this series privately.

Oleg.

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