linux-kernel - Re: 2.6.26-rc9: Reported regressions from 2.6.25

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Message-ID: <20080706165810.GA16189@elte.hu>
Date:	Sun, 6 Jul 2008 18:58:10 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Adrian Bunk <bunk@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Natalie Protasevich <protasnb@...il.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Maximilian Engelhardt <maxi@...monizer.de>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>
Subject: Re: 2.6.26-rc9: Reported regressions from 2.6.25


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=10815
> > Subject		: 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0
> > Submitter	: Alexey Dobriyan <adobriyan@...il.com>
> > Date		: 2008-05-27 09:23 (41 days old)
> > References	: http://lkml.org/lkml/2008/5/27/9
> > 		  http://lkml.org/lkml/2008/6/14/87
> > Handled-By	: Oleg Nesterov <oleg@...sign.ru>
> > 		  Linus Torvalds <torvalds@...ux-foundation.org>
> > 		  Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Patch		: http://lkml.org/lkml/2008/5/28/16
> 
> This one is the same thing that is reported as unresolved, and no, I 
> don't think that existing patch was ever really tested to fix 
> anything. Paul?
> 
> I suspect SRCU will need to be simply marked BROKEN for now, because 
> nobody knows what the problem Alexey sees is. Apparently it's been 
> seen by a few other people too.

I'm not sure it's directly related to SRCU - it can change timings and 
freeing patterns enough to tickle other bugs. Since Alexey Dobriyan has 
reported it - are perhaps namespaces in use during this stress-test? 
Maybe it's some namespaces related bug that is more easily reproduced 
under SRCU - namespaces is not a commonly tested feature.

Also, i've been running rcutorture stress-tests on a number of 
test-systems ever since this got reported (and they are running 
currently as well) and cannot see it - neither could Paul reproduce it.

( and Paul is very good in producing RCU related problems - he's
  triggered and fixed many RCU related problems that no-one else saw
  before. )

	Ingo
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