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

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Date:	Thu, 31 May 2007 16:24:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	john stultz <johnstul@...ibm.com>
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


* 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?

	Ingo
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