Subject: Re: [BUG] futex_unlock_pi() hurts my brain and may cause
	application deadlock
From: john stultz <johnstul@us.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: lkml <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
       Steven Rostedt <rostedt@goodmis.org>,
       Sripathi Kodi <sripathik@in.ibm.com>, Oleg Nesterov <oleg@tv-sign.ru>
In-Reply-To: <20070531142455.GA11310@elte.hu>
References: <1180572567.6126.44.camel@localhost.localdomain>
	 <20070531142455.GA11310@elte.hu>
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Date: Thu, 31 May 2007 07:50:27 -0700
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On Thu, 2007-05-31 at 16:24 +0200, Ingo Molnar wrote:
> * john stultz <johnstul@us.ibm.com> wrote:
> 
> > 	So we've been seeing PI mutex deadlocks with a few of our 
> > applications using the -rt kernel. After narrowing things down, we 
> > were finding that the applications were indirectly calling 
> > futex_unlock_pi(), which on occasion would return -EFAULT, which is 
> > promptly ignored by glibc. This would cause the application to 
> > continue on as if it has unlocked the mutex, until it tried to 
> > reacquire it and deadlock.
> 
> > --- a/kernel/futex.c
> > +++ b/kernel/futex.c
> > @@ -2011,6 +2011,7 @@ pi_faulted:
> >  					 attempt);
> >  		if (ret)
> >  			goto out_unlock;
> > +		uval = 0;
> >  		goto retry_locked;
> 
> this looks good to me. Oleg has posted a few more fixes as well - have 
> you tried those too?

Do you have a URL or subject line for the discussion? 
I'll take a look and give them a whirl.

thanks
-john

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