On Mon, 21 Sep 2015, Davidlohr Bueso wrote:
> As such, weakly ordered archs can benefit from more relaxed use
> of barriers when locking/unlocking.
>
> Signed-off-by: Davidlohr Bueso <dbu...@suse.de>
> ---
> kernel/locking/rtmutex.c | 30 +++++++++++++++++++++---------
> 1 file changed, 21 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 7781d80..226a629 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -74,14 +74,23 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
> * set up.
> */
> #ifndef CONFIG_DEBUG_RT_MUTEXES
> -# define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c)
> +# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n)
> == c)
> +# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n)
> == c)
> +# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n)
> == c)
> +
> +/*
> + * Callers must hold the ->wait_lock -- which is the whole purpose as we
> force
> + * all future threads that attempt to [Rmw] the lock to the slowpath. As such
> + * relaxed semantics suffice.
> + */
> static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
> {
> unsigned long owner, *p = (unsigned long *) &lock->owner;
>
> do {
> owner = *p;
> - } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
> + } while (cmpxchg_relaxed(p, owner,
> + owner | RT_MUTEX_HAS_WAITERS) != owner);
> }
>
> /*
> @@ -121,11 +130,14 @@ static inline bool unlock_rt_mutex_safe(struct rt_mutex
> *lock)
> * lock(wait_lock);
> * acquire(lock);
> */
> - return rt_mutex_cmpxchg(lock, owner, NULL);
> + return rt_mutex_cmpxchg_acquire(lock, owner, NULL);
Why is this acquire?
Thanks,
tglx
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