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locking/rwsem: Drop explicit memory barriers
sh and xtensa seem to be the only architectures which use explicit memory barriers for rw_semaphore operations even though they are not really needed because there is the full memory barrier is always implied by atomic_{inc,dec,add,sub}_return() resp. cmpxchg(). Remove them. Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Chris Zankel <chris@zankel.net> Cc: David S. Miller <davem@davemloft.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Signed-off-by: Jason Low <jason.low2@hp.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tony Luck <tony.luck@intel.com> Cc: linux-alpha@vger.kernel.org Cc: linux-arch@vger.kernel.org Cc: linux-ia64@vger.kernel.org Cc: linux-s390@vger.kernel.org Cc: linux-sh@vger.kernel.org Cc: linux-xtensa@linux-xtensa.org Cc: sparclinux@vger.kernel.org Link: http://lkml.kernel.org/r/1460041951-22347-3-git-send-email-mhocko@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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2 changed files with 4 additions and 24 deletions
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@ -24,9 +24,7 @@
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*/
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static inline void __down_read(struct rw_semaphore *sem)
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{
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if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
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smp_wmb();
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else
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if (atomic_inc_return((atomic_t *)(&sem->count)) <= 0)
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rwsem_down_read_failed(sem);
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}
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@ -37,7 +35,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
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while ((tmp = sem->count) >= 0) {
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if (tmp == cmpxchg(&sem->count, tmp,
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tmp + RWSEM_ACTIVE_READ_BIAS)) {
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smp_wmb();
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return 1;
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}
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}
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@ -53,9 +50,7 @@ static inline void __down_write(struct rw_semaphore *sem)
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tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
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(atomic_t *)(&sem->count));
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if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
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smp_wmb();
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else
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if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
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rwsem_down_write_failed(sem);
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}
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@ -65,7 +60,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
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tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
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RWSEM_ACTIVE_WRITE_BIAS);
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smp_wmb();
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return tmp == RWSEM_UNLOCKED_VALUE;
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}
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@ -76,7 +70,6 @@ static inline void __up_read(struct rw_semaphore *sem)
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{
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int tmp;
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smp_wmb();
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tmp = atomic_dec_return((atomic_t *)(&sem->count));
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if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
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rwsem_wake(sem);
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@ -87,7 +80,6 @@ static inline void __up_read(struct rw_semaphore *sem)
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*/
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static inline void __up_write(struct rw_semaphore *sem)
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{
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smp_wmb();
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if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
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(atomic_t *)(&sem->count)) < 0)
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rwsem_wake(sem);
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@ -108,7 +100,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
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{
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int tmp;
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smp_wmb();
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tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
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if (tmp < 0)
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rwsem_downgrade_wake(sem);
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@ -119,7 +110,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
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*/
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static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
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{
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smp_mb();
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return atomic_add_return(delta, (atomic_t *)(&sem->count));
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}
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@ -29,9 +29,7 @@
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*/
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static inline void __down_read(struct rw_semaphore *sem)
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{
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if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
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smp_wmb();
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else
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if (atomic_add_return(1,(atomic_t *)(&sem->count)) <= 0)
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rwsem_down_read_failed(sem);
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}
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@ -42,7 +40,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
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while ((tmp = sem->count) >= 0) {
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if (tmp == cmpxchg(&sem->count, tmp,
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tmp + RWSEM_ACTIVE_READ_BIAS)) {
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smp_wmb();
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return 1;
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}
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}
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@ -58,9 +55,7 @@ static inline void __down_write(struct rw_semaphore *sem)
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tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
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(atomic_t *)(&sem->count));
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if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
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smp_wmb();
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else
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if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
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rwsem_down_write_failed(sem);
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}
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@ -70,7 +65,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
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tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
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RWSEM_ACTIVE_WRITE_BIAS);
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smp_wmb();
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return tmp == RWSEM_UNLOCKED_VALUE;
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}
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@ -81,7 +75,6 @@ static inline void __up_read(struct rw_semaphore *sem)
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{
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int tmp;
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smp_wmb();
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tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
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if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
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rwsem_wake(sem);
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@ -92,7 +85,6 @@ static inline void __up_read(struct rw_semaphore *sem)
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*/
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static inline void __up_write(struct rw_semaphore *sem)
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{
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smp_wmb();
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if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
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(atomic_t *)(&sem->count)) < 0)
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rwsem_wake(sem);
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@ -113,7 +105,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
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{
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int tmp;
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smp_wmb();
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tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
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if (tmp < 0)
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rwsem_downgrade_wake(sem);
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@ -124,7 +115,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
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*/
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static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
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{
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smp_mb();
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return atomic_add_return(delta, (atomic_t *)(&sem->count));
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}
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