From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@kernel.org>
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=-3.8 required=3.0 tests=BAYES_00,
	HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS
	autolearn=no 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 2AE11C43460
	for <linux-kernel@archiver.kernel.org>; Tue,  6 Apr 2021 14:46:14 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [23.128.96.18])
	by mail.kernel.org (Postfix) with ESMTP id E72BB613C0
	for <linux-kernel@archiver.kernel.org>; Tue,  6 Apr 2021 14:46:13 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1345301AbhDFOqS (ORCPT
        <rfc822;linux-kernel@archiver.kernel.org>);
        Tue, 6 Apr 2021 10:46:18 -0400
Received: from mail.kernel.org ([198.145.29.99]:48168 "EHLO mail.kernel.org"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S233235AbhDFOqQ (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 6 Apr 2021 10:46:16 -0400
Received: by mail.kernel.org (Postfix) with ESMTPSA id E5CF6613C0;
        Tue,  6 Apr 2021 14:46:05 +0000 (UTC)
Date:   Tue, 6 Apr 2021 16:46:02 +0200
From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Jens Axboe <axboe@kernel.dk>,
        syzbot <syzbot+c88a7030da47945a3cc3@syzkaller.appspotmail.com>,
        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: <20210406144602.iqvtsybmhv7ww5en@wittgenstein>
References: <YGs4clcRhyoXX8D0@zeniv-ca.linux.org.uk>
 <20210405170801.zrdhnon6g4ggb6c7@wittgenstein>
 <YGtVtfbYXck3qPRl@zeniv-ca.linux.org.uk>
 <YGtW5g6EFFArtevk@zeniv-ca.linux.org.uk>
 <20210405200737.qurhkqitoxweousx@wittgenstein>
 <YGu7n+dhMep1741/@zeniv-ca.linux.org.uk>
 <20210406123505.auxqtquoys6xg6yf@wittgenstein>
 <YGxeaTzdnxn/3dsY@zeniv-ca.linux.org.uk>
 <20210406132205.qnherkzif64xmgxg@wittgenstein>
 <YGxs5b0pY4esY7J7@zeniv-ca.linux.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <YGxs5b0pY4esY7J7@zeniv-ca.linux.org.uk>
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Apr 06, 2021 at 02:15:01PM +0000, Al Viro wrote:
> On Tue, Apr 06, 2021 at 03:22:05PM +0200, Christian Brauner wrote:
> 
> > 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.
> 
> Because otherwise you either need *all* paths leading to link_path_walk()
> duplicate the logics (and get hurt whenever you miss one) or have "well,
> in some cases link_path_walk() handles ERR_PTR() given to it, in some
> cases its caller do" mess.
> 
> > > >         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?
> 
> I'm referring to the fact that your diff is with an already modified path_lookupat()
> _and_ those modifications have managed to introduce a bug your patch reverts.
> No terminate_walk() paired with that path_init() failure, i.e. path_init() is
> responsible for cleanups on its (many) failure exits...

Note that the paste post the patch was just a doodle to illustrate the
point not sm to review in earnest (I should probably comment prefix
things like this with "untested".).