linux-kernel - Re: [PATCH v3 2/3] mutex: add support for wound/wait style locks, v3

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Date:	Mon, 27 May 2013 10:00:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	x86@...nel.org, dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org, robclark@...il.com,
	rostedt@...dmis.org, tglx@...utronix.de, mingo@...e.hu,
	linux-media@...r.kernel.org, Dave Airlie <airlied@...hat.com>
Subject: Re: [PATCH v3 2/3] mutex: add support for wound/wait style locks, v3

On Wed, May 22, 2013 at 07:24:38PM +0200, Maarten Lankhorst wrote:
> >> +- Functions to only acquire a single w/w mutex, which results in the exact same
> >> +  semantics as a normal mutex. These functions have the _single postfix.
> > This is missing rationale.

> trylock_single is useful when iterating over a list, and you want to evict a bo, but only the first one that can be acquired.
> lock_single is useful when only a single bo needs to be acquired, for example to lock a buffer during mmap.

OK, so given that its still early, monday and I haven't actually spend
much time thinking on this; would it be possible to make:
ww_mutex_lock(.ctx=NULL) act like ww_mutex_lock_single()?

The idea is that if we don't provide a ctx, we'll get a different
lockdep annotation; mutex_lock() vs mutex_lock_nest_lock(). So if we
then go and make a mistake, lockdep should warn us.

Would that work or should I stock up on morning juice?
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