linux-kernel - Re: [tip:core/locking] locking/mutexes: Unlock the mutex without the wait

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Date:	Wed, 12 Mar 2014 11:44:38 -0700
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/locking] locking/mutexes: Unlock the mutex without
 the wait_lock

On Wed, 2014-03-12 at 13:24 +0100, Peter Zijlstra wrote:
> On Tue, Mar 11, 2014 at 05:41:23AM -0700, tip-bot for Jason Low wrote:
> >  kernel/locking/mutex.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> > index 82dad2c..dc3d6f2 100644
> > --- a/kernel/locking/mutex.c
> > +++ b/kernel/locking/mutex.c
> > @@ -671,10 +671,6 @@ __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
> >  	struct mutex *lock = container_of(lock_count, struct mutex, count);
> >  	unsigned long flags;
> >  
> > -	spin_lock_mutex(&lock->wait_lock, flags);
> > -	mutex_release(&lock->dep_map, nested, _RET_IP_);
> > -	debug_mutex_unlock(lock);
> > -

With the latest patch, perhaps it may be helpful to also add to the
comment below, mentioning that it doesn't unlock here for debug mutexes
since the following debug_mutex_unlock() would handle the unlocking
instead.

> >  	/*
> >  	 * some architectures leave the lock unlocked in the fastpath failure
> >  	 * case, others need to leave it locked. In the later case we have to
> > @@ -683,6 +679,10 @@ __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
> >  	if (__mutex_slowpath_needs_to_unlock())
> >

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