Some architectures may have their special barriers for acquire, release
and fence semantics, so that general memory barriers(smp_mb__*_atomic())
in the default __atomic_op_*() may be too strong, so allow architectures
to define their own helpers which can overwrite the default helpers.
Signed-off-by: Boqun Feng <boqun.f...@gmail.com>
---
include/linux/atomic.h | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index 301de78..5f3ee5a 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -34,20 +34,29 @@
* The idea here is to build acquire/release variants by adding explicit
* barriers on top of the relaxed variant. In the case where the relaxed
* variant is already fully ordered, no additional barriers are needed.
+ *
+ * Besides, if an arch has a special barrier for acquire/release, it could
+ * implement its own __atomic_op_* and use the same framework for building
+ * variants
*/
+#ifndef __atomic_op_acquire
#define __atomic_op_acquire(op, args...) \
({ \
typeof(op##_relaxed(args)) __ret = op##_relaxed(args); \
smp_mb__after_atomic(); \
__ret; \
})
+#endif
+#ifndef __atomic_op_release
#define __atomic_op_release(op, args...) \
({ \
smp_mb__before_atomic(); \
op##_relaxed(args); \
})
+#endif
+#ifndef __atomic_op_fence
#define __atomic_op_fence(op, args...) \
({ \
typeof(op##_relaxed(args)) __ret; \
@@ -56,6 +65,7 @@
smp_mb__after_atomic(); \
__ret; \
})
+#endif
/* atomic_add_return_relaxed */
#ifndef atomic_add_return_relaxed
--
2.6.4
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