xfs: Don't flush stale inodes

Because inodes remain in cache much longer than inode buffers do
under memory pressure, we can get the situation where we have
stale, dirty inodes being reclaimed but the backing storage has
been freed.  Hence we should never, ever flush XFS_ISTALE inodes
to disk as there is no guarantee that the backing buffer is in
cache and still marked stale when the flush occurs.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Alex Elder <aelder@sgi.com>

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index ce278b3ae7fcb607ff1f6d5e9e13b621744e95bb..391d36b0e68c2a33b769dd66540148e94e7da3f2 100644 (file)
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -2841,10 +2841,14 @@ xfs_iflush(
        mp = ip->i_mount;
 
        /*
-        * If the inode isn't dirty, then just release the inode
-        * flush lock and do nothing.
+        * If the inode isn't dirty, then just release the inode flush lock and
+        * do nothing. Treat stale inodes the same; we cannot rely on the
+        * backing buffer remaining stale in cache for the remaining life of
+        * the stale inode and so xfs_itobp() below may give us a buffer that
+        * no longer contains inodes below. Doing this stale check here also
+        * avoids forcing the log on pinned, stale inodes.
         */
-       if (xfs_inode_clean(ip)) {
+       if (xfs_inode_clean(ip) || xfs_iflags_test(ip, XFS_ISTALE)) {
                xfs_ifunlock(ip);
                return 0;
        }