[PATCH 8/8] i386: bitops: smp_mb__{before, after}_clear_bit() definitions

[Satyam Sharma]

From: Satyam Sharma <ssatyam@xxxxxxxxxxxxxx>

[8/8] i386: bitops: smp_mb__{before, after}_clear_bit() definitions

>From Documentation/atomic_ops.txt, those archs that require explicit
memory barriers around clear_bit() must also implement these two interfaces.
However, for i386, clear_bit() is a strict, locked, atomic and
un-reorderable operation and includes an implicit memory barrier already.

But these two functions have been wrongly defined as "barrier()" which is
a pointless _compiler optimization_ barrier, and only serves to make gcc
not do legitimate optimizations that it could have otherwise done.

So let's make these proper no-ops, because that's exactly what we require
these to be on the i386 platform.

Signed-off-by: Satyam Sharma <ssatyam@xxxxxxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>

---

[ A similar optimization needs to be done in the atomic.h also.
  Will submit that patch shortly. ]

 include/asm-i386/bitops.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/asm-i386/bitops.h b/include/asm-i386/bitops.h
index 4f1fda5..42999eb 100644
--- a/include/asm-i386/bitops.h
+++ b/include/asm-i386/bitops.h
@@ -106,8 +106,8 @@ static inline void __clear_bit(int nr, unsigned long *addr)
  * Bit operations are already serializing on x86.
  * These must still be defined here for API completeness.
  */
-#define smp_mb__before_clear_bit()	barrier()
-#define smp_mb__after_clear_bit()	barrier()
+#define smp_mb__before_clear_bit()	do {} while (0)
+#define smp_mb__after_clear_bit()	do {} while (0)
 
 /**
  * __change_bit - Toggle a bit in memory
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/