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>

diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h
index a5104be..f6c951c 100644 (file)
--- a/arch/sh/include/asm/rwsem.h
+++ b/arch/sh/include/asm/rwsem.h
@@ -24,9 +24,7 @@
  */
 static inline void __down_read(struct rw_semaphore *sem)
 {
-       if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
-               smp_wmb();
-       else
+       if (atomic_inc_return((atomic_t *)(&sem->count)) <= 0)
                rwsem_down_read_failed(sem);
 }
 
@@ -37,7 +35,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
        while ((tmp = sem->count) >= 0) {
                if (tmp == cmpxchg(&sem->count, tmp,
                                   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-                       smp_wmb();
                        return 1;
                }
        }
@@ -53,9 +50,7 @@ static inline void __down_write(struct rw_semaphore *sem)
 
        tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
                                (atomic_t *)(&sem->count));
-       if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
-               smp_wmb();
-       else
+       if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
                rwsem_down_write_failed(sem);
 }
 
@@ -65,7 +60,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
 
        tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
                      RWSEM_ACTIVE_WRITE_BIAS);
-       smp_wmb();
        return tmp == RWSEM_UNLOCKED_VALUE;
 }
 
@@ -76,7 +70,6 @@ static inline void __up_read(struct rw_semaphore *sem)
 {
        int tmp;
 
-       smp_wmb();
        tmp = atomic_dec_return((atomic_t *)(&sem->count));
        if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
                rwsem_wake(sem);
@@ -87,7 +80,6 @@ static inline void __up_read(struct rw_semaphore *sem)
  */
 static inline void __up_write(struct rw_semaphore *sem)
 {
-       smp_wmb();
        if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
                              (atomic_t *)(&sem->count)) < 0)
                rwsem_wake(sem);
@@ -108,7 +100,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 {
        int tmp;
 
-       smp_wmb();
        tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
        if (tmp < 0)
                rwsem_downgrade_wake(sem);
@@ -119,7 +110,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
  */
 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 {
-       smp_mb();
        return atomic_add_return(delta, (atomic_t *)(&sem->count));
 }
 

diff --git a/arch/xtensa/include/asm/rwsem.h b/arch/xtensa/include/asm/rwsem.h
index 249619e..593483f 100644 (file)
--- a/arch/xtensa/include/asm/rwsem.h
+++ b/arch/xtensa/include/asm/rwsem.h
@@ -29,9 +29,7 @@
  */
 static inline void __down_read(struct rw_semaphore *sem)
 {
-       if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
-               smp_wmb();
-       else
+       if (atomic_add_return(1,(atomic_t *)(&sem->count)) <= 0)
                rwsem_down_read_failed(sem);
 }
 
@@ -42,7 +40,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
        while ((tmp = sem->count) >= 0) {
                if (tmp == cmpxchg(&sem->count, tmp,
                                   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-                       smp_wmb();
                        return 1;
                }
        }
@@ -58,9 +55,7 @@ static inline void __down_write(struct rw_semaphore *sem)
 
        tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
                                (atomic_t *)(&sem->count));
-       if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
-               smp_wmb();
-       else
+       if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
                rwsem_down_write_failed(sem);
 }
 
@@ -70,7 +65,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
 
        tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
                      RWSEM_ACTIVE_WRITE_BIAS);
-       smp_wmb();
        return tmp == RWSEM_UNLOCKED_VALUE;
 }
 
@@ -81,7 +75,6 @@ static inline void __up_read(struct rw_semaphore *sem)
 {
        int tmp;
 
-       smp_wmb();
        tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
        if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
                rwsem_wake(sem);
@@ -92,7 +85,6 @@ static inline void __up_read(struct rw_semaphore *sem)
  */
 static inline void __up_write(struct rw_semaphore *sem)
 {
-       smp_wmb();
        if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
                              (atomic_t *)(&sem->count)) < 0)
                rwsem_wake(sem);
@@ -113,7 +105,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 {
        int tmp;
 
-       smp_wmb();
        tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
        if (tmp < 0)
                rwsem_downgrade_wake(sem);
@@ -124,7 +115,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
  */
 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 {
-       smp_mb();
        return atomic_add_return(delta, (atomic_t *)(&sem->count));
 }