From 0fb067ba77ab74a298ec1f2e56a6a773613bd359 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 4 Apr 2008 14:38:17 -0700
Subject: [PATCH] --- yaml --- r: 88132 b: refs/heads/master c:
 1be62dc190ebaca331038962c873e7967de6cc4b h: refs/heads/master v: v3

---
 [refs]            |  2 +-
 trunk/fs/buffer.c | 15 ++++++++++++++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/[refs] b/[refs]
index 2a7ca63def8a..c359b8992ed8 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 4ed919014eb2b591eb8fdd4dd00226a65faddef4
+refs/heads/master: 1be62dc190ebaca331038962c873e7967de6cc4b
diff --git a/trunk/fs/buffer.c b/trunk/fs/buffer.c
index 98196327ddf0..39ff14403d13 100644
--- a/trunk/fs/buffer.c
+++ b/trunk/fs/buffer.c
@@ -1181,7 +1181,20 @@ __getblk_slow(struct block_device *bdev, sector_t block, int size)
 void mark_buffer_dirty(struct buffer_head *bh)
 {
 	WARN_ON_ONCE(!buffer_uptodate(bh));
-	if (!buffer_dirty(bh) && !test_set_buffer_dirty(bh))
+
+	/*
+	 * Very *carefully* optimize the it-is-already-dirty case.
+	 *
+	 * Don't let the final "is it dirty" escape to before we
+	 * perhaps modified the buffer.
+	 */
+	if (buffer_dirty(bh)) {
+		smp_mb();
+		if (buffer_dirty(bh))
+			return;
+	}
+
+	if (!test_set_buffer_dirty(bh))
 		__set_page_dirty(bh->b_page, page_mapping(bh->b_page), 0);
 }