[XFS] Fix memory corruption with small buffer reads

[linux-2.6-omap-h63xx.git] / fs / xfs / linux-2.6 / xfs_buf.h

diff --git a/fs/xfs/linux-2.6/xfs_buf.h b/fs/xfs/linux-2.6/xfs_buf.h
index 841d7883528db8df2455ac50c173ba9ddeb97b1c..f948ec7ba9a4300b2089ff1a4b8b4f3c2dd70ff4 100644 (file)
--- a/fs/xfs/linux-2.6/xfs_buf.h
+++ b/fs/xfs/linux-2.6/xfs_buf.h
@@ -66,6 +66,25 @@ typedef enum {
        _XBF_PAGES = (1 << 18),     /* backed by refcounted pages          */
        _XBF_RUN_QUEUES = (1 << 19),/* run block device task queue         */
        _XBF_DELWRI_Q = (1 << 21),   /* buffer on delwri queue             */
+
+       /*
+        * Special flag for supporting metadata blocks smaller than a FSB.
+        *
+        * In this case we can have multiple xfs_buf_t on a single page and
+        * need to lock out concurrent xfs_buf_t readers as they only
+        * serialise access to the buffer.
+        *
+        * If the FSB size >= PAGE_CACHE_SIZE case, we have no serialisation
+        * between reads of the page. Hence we can have one thread read the
+        * page and modify it, but then race with another thread that thinks
+        * the page is not up-to-date and hence reads it again.
+        *
+        * The result is that the first modifcation to the page is lost.
+        * This sort of AGF/AGI reading race can happen when unlinking inodes
+        * that require truncation and results in the AGI unlinked list
+        * modifications being lost.
+        */
+       _XBF_PAGE_LOCKED = (1 << 22),
 } xfs_buf_flags_t;
 
 typedef enum {