linux-kernel - Re: [PATCH v2 2/3] mutex: add support for reservation style locks, v2

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Date:	Thu, 04 Apr 2013 18:39:44 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	linux-arch@...r.kernel.org, daniel.vetter@...ll.ch, x86@...nel.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org, robclark@...il.com,
	tglx@...utronix.de, mingo@...e.hu, linux-media@...r.kernel.org
Subject: Re: [PATCH v2 2/3] mutex: add support for reservation style locks,
 v2

On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> The trick with the current code is that the oldest task
> will never see an -EAGAIN ever and hence is guaranteed to make forward
> progress. If the task is really unlucky though it might be forced to
> wait
> for a younger task for every ww_mutex it tries to acquire.

Agreed on that.. while I didn't state this my proposed thing should
behave the same. It follows from the symmetry breaking in that only
younger tasks can get 'kill'ed.

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