From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 03EA2C43460 for ; Tue, 6 Apr 2021 13:22:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D7D1B613B8 for ; Tue, 6 Apr 2021 13:22:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242616AbhDFNWY (ORCPT ); Tue, 6 Apr 2021 09:22:24 -0400 Received: from mail.kernel.org ([198.145.29.99]:57326 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231897AbhDFNWS (ORCPT ); Tue, 6 Apr 2021 09:22:18 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5A3FA613B8; Tue, 6 Apr 2021 13:22:08 +0000 (UTC) Date: Tue, 6 Apr 2021 15:22:05 +0200 From: Christian Brauner To: Al Viro Cc: Jens Axboe , syzbot , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, io-uring@vger.kernel.org Subject: Re: [syzbot] WARNING in mntput_no_expire (2) Message-ID: <20210406132205.qnherkzif64xmgxg@wittgenstein> References: <20210405114437.hjcojekyp5zt6huu@wittgenstein> <20210405170801.zrdhnon6g4ggb6c7@wittgenstein> <20210405200737.qurhkqitoxweousx@wittgenstein> <20210406123505.auxqtquoys6xg6yf@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 06, 2021 at 01:13:13PM +0000, Al Viro wrote: > On Tue, Apr 06, 2021 at 02:35:05PM +0200, Christian Brauner wrote: > > > And while we're at it might I bring up the possibility of an additional > > cleanup of how we currently call path_init(). > > Right now we pass the return value from path_init() directly into e.g. > > link_path_walk() which as a first thing checks for error. Which feels > > rather wrong and has always confused me when looking at these codepaths. > > Why? Why is a another function in charge of checking the return value of an initialization function. If something like path_init() fails why is the next caller responsible for rejecting it's return value and then we're passing that failure value through the whole function with if (!err) ladders but as I said it's mostly style preferences. > > > I get that it might make sense for reasons unrelated to path_init() that > > link_path_walk() checks its first argument for error but path_init() > > should be checked for error right away especially now that we return > > early when LOOKUP_CACHED is set without LOOKUP_RCU. > > But you are making the _callers_ of path_init() do that, for no good > reason. I'm confused why having callers of functions responsible for checking error values is such an out-of-band concept suddenly. I don't think it's worth arguing over this though. > > > thing especially in longer functions such as path_lookupat() where it > > gets convoluted pretty quickly. I think it would be cleaner to have > > something like [1]. The early exists make the code easier to reason > > about imho. But I get that that's a style discussion. > > Your variant is a lot more brittle, actually. > > > @@ -2424,33 +2424,49 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path > > int err; > > > > s = path_init(nd, flags); > > - if (IS_ERR(s)) > > - return PTR_ERR(s); > > Where has that come from, BTW? Currently path_lookupat() does no such thing. Hm? Are you maybe overlooking path_init() which assigns straight into the variable declaration? Or are you referring to sm else? static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path) { const char *s = path_init(nd, flags); int err; if (unlikely(flags & LOOKUP_DOWN) && !IS_ERR(s)) { err = handle_lookup_down(nd); if (unlikely(err < 0)) s = ERR_PTR(err); } while (!(err = link_path_walk(s, nd)) && (s = lookup_last(nd)) != NULL) ;