[XFS] Add back a missing pflags check in releasepage.

SGI Modid: xfs-linux:xfs-kern:166323a

fs/xfs/linux/xfs_aops.c

@@ -410,7 +410,6 @@ map_unwritten(
 	/* get an "empty" pagebuf to manage IO completion
 	 * Proper values will be set before returning */
 	pb = pagebuf_lookup(iomapp->iomap_target, 0, 0, 0);
-
 	if (!pb)
 		return -EAGAIN;
 
@@ -1183,6 +1182,12 @@ linvfs_release_page(
 	if (!(gfp_mask & __GFP_FS))
 		return 0;
 
+	/* If we are already inside a transaction or the thread cannot
+	 * do I/O, we cannot release this page.
+	 */
+	if (PFLAGS_TEST_FSTRANS())
+		return 0;
+
 	/*
 	 * Convert delalloc space to real space, do not flush the
 	 * data out to disk, that will be done by the caller.