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
--- 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 @@
while ((tmp = sem->count) >= 0) {
if (tmp == cmpxchg(&sem->count, tmp,
tmp + RWSEM_ACTIVE_READ_BIAS)) {
- smp_wmb();
return 1;
}
}
@@ -53,9 +50,7 @@
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 @@
tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
- smp_wmb();
return tmp == RWSEM_UNLOCKED_VALUE;
}
@@ -76,7 +70,6 @@
{
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_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 @@
{
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 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
--- 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 @@
while ((tmp = sem->count) >= 0) {
if (tmp == cmpxchg(&sem->count, tmp,
tmp + RWSEM_ACTIVE_READ_BIAS)) {
- smp_wmb();
return 1;
}
}
@@ -58,9 +55,7 @@
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 @@
tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
- smp_wmb();
return tmp == RWSEM_UNLOCKED_VALUE;
}
@@ -81,7 +75,6 @@
{
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_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 @@
{
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 int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
{
- smp_mb();
return atomic_add_return(delta, (atomic_t *)(&sem->count));
}