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

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Date:	Tue, 19 Jan 2010 20:53:14 -0800
From:	Andrew Athan <linux_kernel_aathan@...eplex.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Andrew Athan <linux_kernel_aathan@...eplex.com>,
	linux-kernel@...r.kernel.org, Darren Hart <dvhltc@...ibm.com>,
	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:
> 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.  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.

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

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