Re: [PATCH] mutex: set owner only once on acquisition

[Johannes Weiner <hannes@cmpxchg.org>]

On Thu, Jan 15, 2009 at 09:41:01AM +0100, Johannes Weiner wrote:
> mutex_lock() sets the lock owner, no need to set it upfront in
> __mutex_lock_common().
> 
> Inside __mutex_lock_common() we can cope with the case where the
> successful acquirer got preempted by us before setting the owner
> field: there is an explicit check in the spinning code and the
> sleeping part doesn't rely on it.
> 
> The debug code does owner checks only on unlock where the field is
> garuanteed to be set.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  kernel/mutex.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> Just a small observation.  Peter said it wouldn't matter much as the
> write is to a hot cache line.  But otoh, why keep it if it's not
> necessary. :)

Damn, I'm really async here, sorry Peter.  Just noticed you already
picked it up.

	Hannes