Re: [PATCH -v4 2/8] locking/mutex: Rework mutex::owner

[Davidlohr Bueso]

On Fri, 07 Oct 2016, Peter Zijlstra wrote:
> +/*
> + * Optimistic trylock that only works in the uncontended case. Make sure to
> + * follow with a __mutex_trylock() before failing.
> + */
> +static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
> +{
> +	unsigned long curr = (unsigned long)current;
> +
> +	if (!atomic_long_cmpxchg_acquire(&lock->owner, 0UL, curr))
> +		return true;

Do we want to do a ccas check for !lock->owner? Although I can see a possible
case of 'optimizing for the contended' reasons for nay.

Thanks,
Davidlohr