fs: buffer lock use lock bitops

trylock_buffer and unlock_buffer open and close a critical section.
Hence, we can use the lock bitops to get the desired memory ordering.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/buffer.c

@@ -76,8 +76,7 @@ EXPORT_SYMBOL(__lock_buffer);
 
 void unlock_buffer(struct buffer_head *bh)
 {
-	smp_mb__before_clear_bit();
-	clear_buffer_locked(bh);
+	clear_bit_unlock(BH_Lock, &bh->b_state);
 	smp_mb__after_clear_bit();
 	wake_up_bit(&bh->b_state, BH_Lock);
 }

include/linux/buffer_head.h

@@ -322,7 +322,7 @@ static inline void wait_on_buffer(struct buffer_head *bh)
 
 static inline int trylock_buffer(struct buffer_head *bh)
 {
-	return likely(!test_and_set_bit(BH_Lock, &bh->b_state));
+	return likely(!test_and_set_bit_lock(BH_Lock, &bh->b_state));
 }
 
 static inline void lock_buffer(struct buffer_head *bh)