linux-kernel - Re: [BUG] futex_unlock_pi() hurts my brain and may cause application deadlock

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Date:	Thu, 31 May 2007 07:50:27 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sripathi Kodi <sripathik@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>
Subject: Re: [BUG] futex_unlock_pi() hurts my brain and may cause
	application deadlock

On Thu, 2007-05-31 at 16:24 +0200, Ingo Molnar wrote:
> * john stultz <johnstul@...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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