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

[Darren Hart]

Andrew Athan wrote:
> Andrew Athan wrote:
> > AmÃrico Wang wrote:
> > > On Tue, Jan 12, 2010 at 10:55 PM, Peter Zijlstra 
> > > <peterz@xxxxxxxxxxxxx> wrote:
> > >  
> > > > On Tue, 2010-01-12 at 22:52 +0800, AmÃrico 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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> > > Please read the FAQ at  http://www.tux.org/lkml/
> > >   
> > 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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