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

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Message-ID: <Pine.LNX.4.58.0707311957530.7904@gandalf.stny.rr.com>
Date:	Tue, 31 Jul 2007 20:00:05 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	john stultz <johnstul@...ibm.com>
cc:	Ingo Molnar <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sripathi Kodi <sripathik@...ibm.com>
Subject: Re: [RESEND] [BUG] futex_unlock_pi() hurts my brain and may cause
 application deadlock



--
On Tue, 31 Jul 2007, john stultz wrote:

> On Wed, 2007-05-30 at 17:49 -0700, john stultz wrote:
>
> Hey Ingo,
> 	I sent this fix for this back in the 2.6.21-rt9 era, and I thought to
> picked it up, but I think it arrived amid some futex churn and
> apparently has been dropped or was just lost.
>
> Some of our testers have been reporting futex deadlocks and this fix
> resolves it, so I believe it to still be needed.

Heh, I remember this bug.  Wasn't there another patch that modified this.
I almost definitly remember this getting into the patch queue, but it must
have been dropped later.

John, thanks for looking into this deeper!

Acked-by: Steven Rostedt <rostedt@...dmis.org>

>
> thanks
> -john
>
> Avoid futex_unlock_pi returning -EFAULT (which results in deadlock), by
> clearing uval before jumping to retry_locked.
>
> Signed-off-by: John Stultz <johnstul@...ibm.com>
> Index: 2.6-rt/kernel/futex.c
> ===================================================================
> --- 2.6-rt.orig/kernel/futex.c	2007-07-31 16:48:41.000000000 -0700
> +++ 2.6-rt/kernel/futex.c	2007-07-31 16:48:48.000000000 -0700
> @@ -1673,6 +1673,7 @@ pi_faulted:
>  					 attempt);
>  		if (ret)
>  			goto out;
> +		uval = 0;
>  		goto retry_unlocked;
>  	}
>
>
>
>
>
-
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