Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1230344

Re: [PATCH 3/5] locking/rtmutex: Use acquire/release semantics

Show all headers | View raw

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 <dbueso@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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 0/5] locking: Use acquire/release semantics Davidlohr Bueso <dave@stgolabs.net> - 2015-09-21 22:20 +0200
  [PATCH 4/5] locking/rwsem: Use acquire/release semantics Davidlohr Bueso <dave@stgolabs.net> - 2015-09-21 22:20 +0200
    Re: [PATCH 4/5] locking/rwsem: Use acquire/release semantics Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-21 22:40 +0200
    [PATCH v2] locking/rwsem: Use acquire/release semantics Davidlohr Bueso <dave@stgolabs.net> - 2015-09-24 03:10 +0200
  [PATCH 3/5] locking/rtmutex: Use acquire/release semantics Davidlohr Bueso <dave@stgolabs.net> - 2015-09-21 22:20 +0200
    Re: [PATCH 3/5] locking/rtmutex: Use acquire/release semantics Thomas Gleixner <tglx@linutronix.de> - 2015-09-22 17:40 +0200
      Re: [PATCH 3/5] locking/rtmutex: Use acquire/release semantics Davidlohr Bueso <dave@stgolabs.net> - 2015-09-22 18:00 +0200
    [PATCH v2] locking/rtmutex: Use acquire/release semantics Davidlohr Bueso <dave@stgolabs.net> - 2015-09-24 03:10 +0200
      Re: [PATCH v2] locking/rtmutex: Use acquire/release semantics Thomas Gleixner <tglx@linutronix.de> - 2015-09-27 12:40 +0200
        Re: [PATCH v2] locking/rtmutex: Use acquire/release semantics Davidlohr Bueso <dave@stgolabs.net> - 2015-09-28 22:00 +0200
          Re: [PATCH v2] locking/rtmutex: Use acquire/release semantics Thomas Gleixner <tglx@linutronix.de> - 2015-09-29 23:00 +0200
  [PATCH 1/5] asm-generic: Add _{relaxed|acquire|release}() variants for inc/dec atomics Davidlohr Bueso <dave@stgolabs.net> - 2015-09-21 22:20 +0200

csiph-web