Be more careful about marking buffers dirty

[sfrench/cifs-2.6.git] / fs / buffer.c

diff --git a/fs/buffer.c b/fs/buffer.c
index 7ba58386beee459779da2056d662572496ff2096..39ff14403d137be85dcd11161584abeabd9d7577 100644 (file)
--- 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);