From 5a8897cc7631fa544d079c443800f4420d1b173f Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 24 Oct 2017 11:22:50 +0100 Subject: locking/atomics/alpha: Add smp_read_barrier_depends() to _release()/_relaxed() atomics As part of the fight against smp_read_barrier_depends(), we require dependency ordering to be preserved when a dependency is headed by a load performed using an atomic operation. This patch adds smp_read_barrier_depends() to the _release() and _relaxed() atomics on alpha, which otherwise lack anything to enforce dependency ordering. Signed-off-by: Will Deacon Signed-off-by: Paul E. McKenney Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1508840570-22169-6-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar --- arch/alpha/include/asm/atomic.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'arch/alpha') diff --git a/arch/alpha/include/asm/atomic.h b/arch/alpha/include/asm/atomic.h index 498933a7df97..16961a3f45ba 100644 --- a/arch/alpha/include/asm/atomic.h +++ b/arch/alpha/include/asm/atomic.h @@ -13,6 +13,15 @@ * than regular operations. */ +/* + * To ensure dependency ordering is preserved for the _relaxed and + * _release atomics, an smp_read_barrier_depends() is unconditionally + * inserted into the _relaxed variants, which are used to build the + * barriered versions. To avoid redundant back-to-back fences, we can + * define the _acquire and _fence versions explicitly. + */ +#define __atomic_op_acquire(op, args...) op##_relaxed(args) +#define __atomic_op_fence __atomic_op_release #define ATOMIC_INIT(i) { (i) } #define ATOMIC64_INIT(i) { (i) } @@ -60,6 +69,7 @@ static inline int atomic_##op##_return_relaxed(int i, atomic_t *v) \ ".previous" \ :"=&r" (temp), "=m" (v->counter), "=&r" (result) \ :"Ir" (i), "m" (v->counter) : "memory"); \ + smp_read_barrier_depends(); \ return result; \ } @@ -77,6 +87,7 @@ static inline int atomic_fetch_##op##_relaxed(int i, atomic_t *v) \ ".previous" \ :"=&r" (temp), "=m" (v->counter), "=&r" (result) \ :"Ir" (i), "m" (v->counter) : "memory"); \ + smp_read_barrier_depends(); \ return result; \ } @@ -111,6 +122,7 @@ static __inline__ long atomic64_##op##_return_relaxed(long i, atomic64_t * v) \ ".previous" \ :"=&r" (temp), "=m" (v->counter), "=&r" (result) \ :"Ir" (i), "m" (v->counter) : "memory"); \ + smp_read_barrier_depends(); \ return result; \ } @@ -128,6 +140,7 @@ static __inline__ long atomic64_fetch_##op##_relaxed(long i, atomic64_t * v) \ ".previous" \ :"=&r" (temp), "=m" (v->counter), "=&r" (result) \ :"Ir" (i), "m" (v->counter) : "memory"); \ + smp_read_barrier_depends(); \ return result; \ } -- cgit