gfs2: Make sure not to return short direct writes

When direct writes fail with -ENOTBLK because we're writing into a
hole (gfs2_iomap_begin()) or because of a page invalidation failure
(iomap_dio_rw()), we're falling back to buffered writes.  In that case,
when we lose the inode glock in gfs2_file_buffered_write(), we want to
re-acquire it instead of returning a short write.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/file.c

@@ -1069,7 +1069,7 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb,
 			from->count = min(from->count, window_size - leftover);
 			if (gfs2_holder_queued(gh))
 				goto retry_under_glock;
-			if (read)
+			if (read && !(iocb->ki_flags & IOCB_DIRECT))
 				goto out_uninit;
 			goto retry;
 		}