Date: Tue, 22 Mar 2005 01:34:05 -0500
From: Jakub Jelinek <jakub@redhat.com>
To: Lee Revell <rlrevell@joe-job.com>
Cc: Andrew Morton <akpm@osdl.org>, Jamie Lokier <jamie@shareable.org>,
       linux-kernel@vger.kernel.org, mingo@elte.hu,
       Chris Morgan <cmorgan@alum.wpi.edu>, paul@linuxaudiosystems.com,
       seto.hidetoshi@jp.fujitsu.com
Subject: Re: kernel bug: futex_wait hang
Message-ID: <20050322063405.GN32746@devserv.devel.redhat.com>
Reply-To: Jakub Jelinek <jakub@redhat.com>
References: <1111463950.3058.20.camel@mindpipe> <20050321202051.2796660e.akpm@osdl.org> <20050322044838.GB32432@mail.shareable.org> <20050321210802.14be70cc.akpm@osdl.org> <1111469453.3563.0.camel@mindpipe>
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On Tue, Mar 22, 2005 at 12:30:53AM -0500, Lee Revell wrote:
> On Mon, 2005-03-21 at 21:08 -0800, Andrew Morton wrote:
> > Jamie Lokier <jamie@shareable.org> wrote:
> > > 
> > > The most recent messages under "Futex queue_me/get_user ordering",
> > > with a patch from Jakub Jelinek will fix this problem by changing the
> > > kernel.  Yes, you should apply Jakub's most recent patch, message-ID
> > > "<20050318165326.GB32746@devserv.devel.redhat.com>".
> > > 
> > > I have not tested the patch, but it looks convincing.
> > 
> > OK, thanks.  Lee && Paul, that's at
> > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.12-rc1/2.6.12-rc1-mm1/broken-out/futex-queue_me-get_user-ordering-fix.patch
> > 
> 
> Does not fix the problem.

Have you analyzed the use of mutexes/condvars in the program?
The primary suspect is a deadlock, race of some kind or other bug
in the program.  All these will show up as a hang in FUTEX_WAIT.
The argument that it works with LinuxThreads doesn't count,
the timing and internals of both threading libraries are so different
that a program bug can only show up with one of the threading libraries
and not both.
Only once you distill a minimal self-contained testcase that proves
the program is correct and it gets analyzed, it is time to talk about
NPTL or kernel bugs.

	Jakub
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