linux-kernel - Re: [Bug #10815] 2.6.26-rc4: RIP find_pid

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Date:	Tue, 24 Jun 2008 11:51:10 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>, Adrian Bunk <bunk@...nel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org
Subject: Re: [Bug #10815] 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0

On Tuesday 24 June 2008 11:31, Linus Torvalds wrote:
> On Tue, 24 Jun 2008, Alexey Dobriyan wrote:
> > Status update:
> > * bug is reproduced on another box with the very same symptoms:
> >   SMP=y, maxcpus=1 kernel occasionally fails, SMP=n is fine.
> >   Also Core 2 Duo, x86_64 [1]
> >
> >   Race is wide -- 60 seconds of rcutorture is enough.
>
> Very odd how you can reproduce it - now on two machines - but it doesn't
> seem to happen for others. You've tried different compilers, you've tried
> different config options, what the heck is left?

The PREEMPT_RCU thing? I've reproduced it. It hits lockless pagecache,
but I've also reproduced the same problem in dentry cache shrinking.
I'm sure it is a free-before-grace bug.

I've been using DEBUG_PAGEALLOC to make it easier to spot.
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