[PATCH/RFC] asm-generic/mutex-dec.h: add SMP support

[Mike Frysinger <vapier@gentoo.org>]

To make these guys work on SMP systems, we just need to sprinkle a few
barriers around.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
---
note: this is what the Blackfin SMP port is using, but it doesn't seem
like other SMP ports are ... so I wonder if we're just trying too hard
and these barriers aren't actually necessary ?

 include/asm-generic/mutex-dec.h |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/include/asm-generic/mutex-dec.h b/include/asm-generic/mutex-dec.h
index f104af7..e746c3c 100644
--- a/include/asm-generic/mutex-dec.h
+++ b/include/asm-generic/mutex-dec.h
@@ -22,6 +22,8 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
 {
 	if (unlikely(atomic_dec_return(count) < 0))
 		fail_fn(count);
+	else
+		smp_mb();
 }
 
 /**
@@ -39,6 +41,7 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
 {
 	if (unlikely(atomic_dec_return(count) < 0))
 		return fail_fn(count);
+	smp_mb();
 	return 0;
 }
 
@@ -58,6 +61,7 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
 static inline void
 __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
 {
+	smp_mb();
 	if (unlikely(atomic_inc_return(count) <= 0))
 		fail_fn(count);
 }
@@ -82,8 +86,10 @@ __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
 static inline int
 __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
 {
-	if (likely(atomic_cmpxchg(count, 1, 0) == 1))
+	if (likely(atomic_cmpxchg(count, 1, 0) == 1)) {
+		smp_mb();
 		return 1;
+	}
 	return 0;
 }
 
-- 
1.7.5.rc3