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SubjectRe: Futex hang/lockup problem in 2.6.30+ on AMD64
Andrew Athan wrote:
> Andrew Athan wrote:
>> Américo Wang wrote:
>>> On Tue, Jan 12, 2010 at 10:55 PM, Peter Zijlstra
>>> <peterz@infradead.org> wrote:
>>>
>>>> On Tue, 2010-01-12 at 22:52 +0800, Américo Wang wrote:
>>>>
>>>>
>>>>>> $ uname -a
>>>>>> Linux UK22 2.6.30-2-amd64 #1 SMP Fri Sep 25 22:16:56 UTC 2009 x86_64
>>>>>> GNU/Linux
>>>>>>
>>>> Does a recent kernel work?
>>>>
>>>>
>>>>
>>>
>>> Ah, I just wanted to ask the same question, adding the original reporter
>>> Gong Cheng into Cc...
>>>
>>> Gong, could you reproduce it on the latest kernel? And what is your
>>> .config?
>>>
>>> Thanks!
>>> --
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>>>
>> Due to remote location of the hardware and I haven't been able to test
>> a more recent (or older) kernel. Remote hands have put a KVM on the
>> box as of an hour ago, so I hope to have some information for you in a
>> day or two.
>>
>> A.
>>
>
>
> I wanted to report that although I have had no luck (so far) running
> anything more recent than 2.6.30, I was able to revert to 2.6.26.
> Unfortunately, the application hang still occurs. I also saw a similar
> hang of the application running on a 32 bit Intel box, also under
> 2.6.26. So far, the hang *always* involves threads stuck on
> pthread_cond_broadcast()'s condition variable's internal lock while
> other threads are waiting on the outer "public" lock.


Are you using real-time scheduling policy or priority inheritance
(PTHREAD_PRIO_INHERIT)? It is possible to suffer an unbounded priority
inversion on the internal condvar data lock in the current distro
implementations of glibc.


> These other
> threads are *not* yet (nor about to) pthread_cond_wait(). I saw a
> message from Darren Hart (subject "Re: Problems with futex") in response
> to someone who apparently was having futex problems in 2.6.27, so I'm
> still operating under the assumption that this is not an application bug.

Those all turned out to be application issues with one exception which
had already been fixed upstream.


> Over the next couple of days, I will be running a version of the
> application in which I replaced the pthread_cond calls with simpler
> locks, in the hopes that it won't hang (because I'm hoping the
> underlying implementation in pthreads uses a different set of futex
> opcodes).
>
> Andrew Athan
>


--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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