Re: [PATCH v2 3/4] mutex: Try to acquire mutex only if it is unlocked

[Davidlohr Bueso <davidlohr@hp.com>]

On Wed, 2014-06-11 at 11:37 -0700, Jason Low wrote:
> Upon entering the slowpath in __mutex_lock_common(), we try once more to
> acquire the mutex. We only try to acquire if (lock->count >= 0). However,
> what we actually want here is to try to acquire if the mutex is unlocked
> (lock->count == 1). 
>   
> This patch changes it so that we only try-acquire the mutex upon entering
> the slowpath if it is unlocked, rather than if the lock count is non-negative.
> This helps further reduce unnecessary atomic xchg() operations.
> 
> Furthermore, this patch uses !mutex_is_locked(lock) to do the initial
> checks for if the lock is free rather than directly calling atomic_read()
> on the lock->count, in order to improve readability.

I think this patch can be merged in 2/4, like you had in v1. Otherwise
looks good.