Message-ID: <1365094158.2609.119.camel@laptop>
Subject: Re: [PATCH v2 2/3] mutex: add support for reservation style locks,
 v2
From: Peter Zijlstra <peterz@infradead.org>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com>,
        linux-arch@vger.kernel.org, daniel.vetter@ffwll.ch, x86@kernel.org,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linaro-mm-sig@lists.linaro.org, robclark@gmail.com, tglx@linutronix.de,
        mingo@elte.hu, linux-media@vger.kernel.org
Date: Thu, 04 Apr 2013 18:49:18 +0200
In-Reply-To: <20130404133123.GW2228@phenom.ffwll.local>
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	 <20130228102502.15191.14146.stgit@patser>
	 <1364900432.18374.24.camel@laptop> <515AF1C1.7080508@canonical.com>
	 <1364921954.20640.22.camel@laptop> <1365076908.2609.94.camel@laptop>
	 <20130404133123.GW2228@phenom.ffwll.local>
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On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> We've discussed this approach of using (rt-prio, age) instead of just
> age
> to determine the the "oldness" of a task for deadlock-breaking with
> -EAGAIN. The problem is that through PI boosting or normal rt-prio
> changes
> while tasks are trying to acquire ww_mutexes you can create acyclic
> loops
> in the blocked-on graph of ww_mutexes after the fact and so cause
> deadlocks. So we've convinced ourselves that this approche doesn't
> work.

Could you pretty please draw me a picture, I'm having trouble seeing
what you mean.

AFAICT as long as you boost Y while its the lock owner things should
work out, no?


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