[patch] buffer: memorder fix

[Nick Piggin]

Anyone mind telling me why unlock_buffer, unlike unlock_page, thinks it can
clear the lock without ensuring the critical section is closed (ie. with a
barrier)?

Signed-off-by: Nick Piggin <npiggin@xxxxxxx>

Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c
+++ linux-2.6/fs/buffer.c
@@ -78,6 +78,7 @@ EXPORT_SYMBOL(__lock_buffer);
 
 void fastcall unlock_buffer(struct buffer_head *bh)
 {
+	smp_mb__before_clear_bit();
 	clear_buffer_locked(bh);
 	smp_mb__after_clear_bit();
 	wake_up_bit(&bh->b_state, BH_Lock);
-
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