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Date: Wed, 27 May 2009 22:34:05 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Paul Smith <paul@mad-scientist.net>
Cc: Andi Kleen <andi@firstfloor.org>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@linux-foundation.org>,
       Roland McGrath <roland@redhat.com>
Subject: Re: [2.6.27.24] Kernel coredump to a pipe is failing
Message-ID: <20090527203405.GA3296@redhat.com>
References: <1243355634.29250.331.camel@psmith-ubeta.netezza.com> <878wkjobbm.fsf@basil.nowhere.org> <20090527183109.GA30574@redhat.com> <20090527185056.GW1065@one.firstfloor.org> <20090527190513.GA32452@redhat.com> <1243453783.29250.434.camel@psmith-ubeta.netezza.com>
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On 05/27, Paul Smith wrote:
>
> On Wed, 2009-05-27 at 21:05 +0200, Oleg Nesterov wrote:
> > On 05/27, Andi Kleen wrote:
> > >
> > > > Actually, I think there is a strong reason to handle signals during
> > > > core dumping. The coredump can take a lot of time/resources, not good
> > > > it looks like unkillable procees to users.
> > >
> > > One problem with that is if you send a process a string of signals that cause
> > > a core dump and then kill. In the old case you would just get a full core dump
> > > on the first signal and be done. With your change it would process
> > > the second signal too and stop the dumping and you get none or a partial
> > > core dump. That might well break existing setups.
> >
> > I don't think we should worry about this particular case. Suppose a user
> > does
> >
> > 	kill(pid, SIGQUIT);
> > 	kill(pid, SIGKILL);
>
> I'm not sure about this.  Why even bother with SIGQUIT (or anything
> else) if you're just going to immediately SIGKILL afterwards?

Probably I misunderstood what Andi meant.

> What
> people do all the time, and I think should be supported, is something
> like this:
>
> 	<do 5 times>
> 		kill(pid, SIGINT);
> 		sleep(1);
> 		<if pid is dead break>
> 	kill(pid, SIGKILL);
>
> Often with other signals in the mix like SIGHUP or whatever.  The idea
> is to give the process a chance to do "whatever it does" to clean up and
> then, if it's still there we consider it too wedged to respond and send
> a SIGKILL.  If the cleanup operations invoked by receiving the SIGINT
> caused a core dump, then you wouldn't want the SIGKILL to stop the core
> dump.

Yes. Once again, this change is user-visble and it can confuse/break
existing setups, I agree. As almost any user-visible change ;)

> On the other hand I do agree that it would be nice to be able to smash a
> core dump that was taking a long time or trying to write to an
> unavailable resource like a stalled NFS mount or whatever.  Sigh.

Yes.

Oleg.