linux-kernel - [patch] buffer: memorder fix

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Message-ID: <20070120070546.GC30774@wotan.suse.de>
Date:	Sat, 20 Jan 2007 08:05:46 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Andrew Morton <akpm@...l.org>, Linus Torvalds <torvalds@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: [patch] buffer: memorder fix


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@...e.de>

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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