linux-kernel - Re: [PATCH] mutex: enable spinning for DEBUG

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Date:	Thu, 19 Feb 2009 12:22:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] mutex: enable spinning for DEBUG_MUTEX


* Peter Zijlstra <peterz@...radead.org> wrote:

> Subject: mutex: enable spinning for DEBUG_MUTEX
> From: Johannes Weiner <hannes@...xchg.org>
> Date: Thu, 15 Jan 2009 15:57:38 +0100
> 
> Spinning with CONFIG_DEBUG_MUTEX is possible but care must be taken
> with the debug checks vs. racy access to the lock owner field.
> 
> In the case where the lock owner gets rescheduled after acquisition
> and therefor unlocks on another CPU, that second CPU might not see the
> write of the owner field from the first CPU and we warn about owner
> mismatch.  Thus the memory barriers for the debug case.
> 
> Also remove the redundant mutex_set_owner()s in __mutex_lock_common()
> and __mutex_trylock_slowpath(), it's taken care of in mutex_lock() and
> mutex_trylock().
> 
> [a.p.zijlstra@...llo.nl: fix _nested variants]
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  kernel/mutex-debug.c |    6 ++++++
>  kernel/mutex-debug.h |    6 ++++++
>  kernel/mutex.c       |   27 +++++++++++++++------------
>  3 files changed, 27 insertions(+), 12 deletions(-)

Applied to tip:core/locking, thanks Peter!

	Ingo
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