linux-kernel - Re: [PATCH] robust futex thread exit race

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Date:	Sun, 30 Sep 2007 17:57:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Ulrich Drepper <drepper@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] robust futex thread exit race


* Thomas Gleixner <tglx@...utronix.de> wrote:

> 
> On Sun, 30 Sep 2007, Ingo Molnar wrote:
> > * Martin Schwidefsky <schwidefsky@...ibm.com> wrote:
> > 
> > > Hi Ingo,
> > > I finally found the bug that causes tst-robust8 from the glibc to fail
> > > on s390x. Turned out to be a common code problem with the processing of
> > > the robust futex list. The patch below fixes the bug for me.
> > 
> > good catch! A quick preliminary review of your patch indicates it's fine 
> > - and it might be v2.6.23 material.
> > 
> > Acked-by: Ingo Molnar <mingo@...e.hu>
> 
>   Acked-by: Thomas Gleixner <tglx@...utronix.de>
>  
> > > Calling handle_futex_death in exit_robust_list for the different 
> > > robust mutexes of a thread basically frees the mutex. Another thread 
> > > might grab the lock immediately which updates the next pointer of the 
> > > mutex. fetch_robust_entry over the next pointer might therefore branch 
> > > into the robust mutex list of a different thread. This can cause two 
> > > problems: 1) some mutexes held by the dead thread are not getting 
> > > freed and 2) some mutexs held by a different thread are freed. The 
> > > next point need to be read before calling handle_futex_death.
> > 
> > nasty race... Ulrich, Thomas, do you concur?
> 
> Yes. Where do they sell those brown paperbags again ?

i've still got plenty of them stacked up, can pass over a few. (i'm 
getting them cheap from the manufacturer - large quantity discount)

	Ingo
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