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-rw-r--r--fs/buffer.c15
1 files changed, 14 insertions, 1 deletions
diff --git a/fs/buffer.c b/fs/buffer.c
index 98196327ddf..39ff14403d1 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);
}