[PATCH] Fix use after free when closing log/rt devices

[Lachlan McIlroy <lachlan@sgi.com>]

The call to xfs_free_buftarg() will free the memory used by it's argument
so we need to save the bdev to pass to xfs_blkdev_put()

Lachlan

--- fs/xfs/linux-2.6/xfs_super.c_1.432	2008-06-27 14:51:17.000000000 +1000
+++ fs/xfs/linux-2.6/xfs_super.c	2008-06-27 14:59:26.000000000 +1000
@@ -781,13 +781,17 @@ STATIC void
 xfs_close_devices(
 	struct xfs_mount	*mp)
 {
+	struct block_device	*bdev;
+
 	if (mp->m_logdev_targp && mp->m_logdev_targp != mp->m_ddev_targp) {
+		bdev = mp->m_logdev_targp->bt_bdev;
 		xfs_free_buftarg(mp->m_logdev_targp);
-		xfs_blkdev_put(mp->m_logdev_targp->bt_bdev);
+		xfs_blkdev_put(bdev);
 	}
 	if (mp->m_rtdev_targp) {
+		bdev = mp->m_rtdev_targp->bt_bdev;
 		xfs_free_buftarg(mp->m_rtdev_targp);
-		xfs_blkdev_put(mp->m_rtdev_targp->bt_bdev);
+		xfs_blkdev_put(bdev);
 	}
 	xfs_free_buftarg(mp->m_ddev_targp);
 }