1 files changed, 20 insertions, 8 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 7ba58386beee..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);
 }
 
@@ -2564,14 +2577,13 @@ int nobh_write_end(struct file *file, struct address_space *mapping,
         struct inode *inode = page->mapping->host;
         struct buffer_head *head = fsdata;
         struct buffer_head *bh;
+        BUG_ON(fsdata != NULL && page_has_buffers(page));
 
-        if (!PageMappedToDisk(page)) {
-                if (unlikely(copied < len) && !page_has_buffers(page))
-                        attach_nobh_buffers(page, head);
-                if (page_has_buffers(page))
-                        return generic_write_end(file, mapping, pos, len,
-                                                copied, page, fsdata);
-        }
+        if (unlikely(copied < len) && !page_has_buffers(page))
+                attach_nobh_buffers(page, head);
+        if (page_has_buffers(page))
+                return generic_write_end(file, mapping, pos, len,
+                                        copied, page, fsdata);
 
         SetPageUptodate(page);
         set_page_dirty(page);