1 files changed, 14 insertions, 1 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 98196327ddf0..39ff14403d13 100644
--- a/fs/buffer.c
+++ b/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);
 }