linux-kernel - Re: Futex hang/lockup problem in 2.6.30+ on AMD64

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Date:	Wed, 20 Jan 2010 09:54:33 -0800
From:	Darren Hart <dvhltc@...ibm.com>
To:	Andrew Athan <linux_kernel_aathan@...eplex.com>
CC:	Américo Wang <xiyou.wangcong@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Gong Cheng <chengg11@...oo.com>
Subject: Re: 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@...radead.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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