linux-kernel - Re: [RFC PATCH] rtmutex: Do not prio boost when timeout is used

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Message-ID: <20140426071702.2a866fc5@gandalf.local.home>
Date:	Sat, 26 Apr 2014 07:17:02 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC PATCH] rtmutex: Do not prio boost when timeout is used

On Sat, 26 Apr 2014 13:04:37 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, Apr 25, 2014 at 04:28:48PM -0400, Steven Rostedt wrote:
> > I've been discussing an issue on IRC with deadlock checking and found
> > something wrong with it. Mainly, if any of the locks have a timeout,
> > then even if the chain loops, there is no real deadlock. If one of the
> > locks in the chain times out, then things will move forward again.
> 
> 
> POSIX (opengroup):
> 
>  http://pubs.opengroup.org/onlinepubs/009695399/functions/pthread_mutex_timedlock.html
> 
> Explicitly states that pthread_mutex_timedlock() should participate in
> the PI chain, it also states that its perfectly valid for this function
> to return -EDEADLK.
> 
> Therefore, there's nothing wrong. If this behaviour breaks userspace,
> its already broken for not actually expecting the right thing.

Fair enough. Thanks for the link.

-- Steve
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