linux-kernel - Re: [patch 1/4] rt-mutex: Fix stale return value

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Date:	Fri, 8 Jun 2007 09:20:50 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [patch 1/4] rt-mutex: Fix stale return value


* Thomas Gleixner <tglx@...utronix.de> wrote:

> -			if (unlikely(!waiter.task))
> +			if (unlikely(!waiter.task)) {
> +				/*
> +				 * Reset the return value. We might
> +				 * have returned with -EDEADLK and the
> +				 * owner released the lock while we
> +				 * were walking the pi chain.
> +				 */
> +				ret = 0;
>  				continue;
> -
> +			}

ok - i guess the reason here that we never triggered it in -rt is that 
-EDEADLK is a really rare case that only occurs with pi-futexes (and 
even then, only with buggy userspace or with intentional testcases). 
Plus, lockdep caught most/all of the in-kernel deadlocks before this 
mechanism could catch it.

Acked-by: Ingo Molnar <mingo@...e.hu>

	Ingo
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