vfs: make fchmodat retry once on ESTALE errors

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/open.c

@@ -514,11 +514,16 @@ SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode
 {
 	struct path path;
 	int error;
-
-	error = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
+	unsigned int lookup_flags = LOOKUP_FOLLOW;
+retry:
+	error = user_path_at(dfd, filename, lookup_flags, &path);
 	if (!error) {
 		error = chmod_common(&path, mode);
 		path_put(&path);
+		if (retry_estale(error, lookup_flags)) {
+			lookup_flags |= LOOKUP_REVAL;
+			goto retry;
+		}
 	}
 	return error;
 }