Re: kernel bug: futex_wait hang

[Jakub Jelinek]

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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxx>".
> > > 
> > > 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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