Re: [PATCH] robust futex thread exit race
From: Thomas Gleixner
Date: Sun Sep 30 2007 - 11:54:12 EST
On Sun, 30 Sep 2007, Ingo Molnar wrote:
> * Martin Schwidefsky <schwidefsky@xxxxxxxxxx> 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@xxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > 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 ?
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