vfs: have do_sys_truncate retry once on an ESTALE error

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

fs/open.c

@@ -115,17 +115,23 @@ EXPORT_SYMBOL_GPL(vfs_truncate);
 
 static long do_sys_truncate(const char __user *pathname, loff_t length)
 {
+	unsigned int lookup_flags = LOOKUP_FOLLOW;
 	struct path path;
 	int error;
 
 	if (length < 0)	/* sorry, but loff_t says... */
 		return -EINVAL;
 
-	error = user_path(pathname, &path);
+retry:
+	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 	if (!error) {
 		error = vfs_truncate(&path, length);
 		path_put(&path);
 	}
+	if (retry_estale(error, lookup_flags)) {
+		lookup_flags |= LOOKUP_REVAL;
+		goto retry;
+	}
 	return error;
 }