Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1755275Ab3JVWDa (ORCPT <rfc822;w@1wt.eu>);
	Tue, 22 Oct 2013 18:03:30 -0400
Received: from ipmail07.adl2.internode.on.net ([150.101.137.131]:9300 "EHLO
	ipmail07.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK)
	by vger.kernel.org with ESMTP id S1754117Ab3JVWD3 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 22 Oct 2013 18:03:29 -0400
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: AqkGALH1ZlJ5LAy1/2dsb2JhbABZgweDTrZJhT+BKxd0giUBAQQBJwsBIxYKAxAIAxgJJQ8FJQMhExUEh2cFuy0WjgeBMQeDH4EKA5gIkgiDOCiBLiQ
Date: Wed, 23 Oct 2013 09:02:54 +1100
From: Dave Chinner <david@fromorbit.com>
To: Eric Sandeen <sandeen@sandeen.net>
Cc: Geyslan =?iso-8859-1?Q?Greg=F3rio?= Bem <geyslan@gmail.com>,
        Ben Myers <bpm@sgi.com>, Alex Elder <elder@kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        XFS FILESYSTEM <xfs@oss.sgi.com>
Subject: Re: [PATCH] xfs: fix possible NULL dereference
Message-ID: <20131022220254.GD2797@dastard>
References: <5265B4D2.3000907@sandeen.net>
 <20131021231849.GL10553@sgi.com>
 <20131021235601.GG4446@dastard>
 <5265C03B.50701@sandeen.net>
 <20131022001732.GI4446@dastard>
 <CAGG-pUTh-PJJ4Nzo0r-f3VDPMc81U2z_NMX+Wcex3KzGs=U8cA@mail.gmail.com>
 <20131022203946.GB2797@dastard>
 <5266E4BD.8030601@sandeen.net>
 <20131022210300.GC2797@dastard>
 <5266EBF0.901@sandeen.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <5266EBF0.901@sandeen.net>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 3927
Lines: 95

On Tue, Oct 22, 2013 at 04:19:44PM -0500, Eric Sandeen wrote:
> On 10/22/13 4:03 PM, Dave Chinner wrote:
> > On Tue, Oct 22, 2013 at 03:49:01PM -0500, Eric Sandeen wrote:
> >> On 10/22/13 3:39 PM, Dave Chinner wrote:
> >>> On Tue, Oct 22, 2013 at 08:12:51AM -0200, Geyslan Greg?rio Bem wrote:
> >>>> 2013/10/21 Dave Chinner <david@fromorbit.com>:
> >>>>> On Mon, Oct 21, 2013 at 07:00:59PM -0500, Eric Sandeen wrote:
> >>>>>> On 10/21/13 6:56 PM, Dave Chinner wrote:
> >>>>>>> On Mon, Oct 21, 2013 at 06:18:49PM -0500, Ben Myers wrote:
> >>>>>
> >>>>> Yes, but to continue the Devil's Advocate argument, the purpose of
> >>>>> debug code isn't to enlightent the casual reader or drive-by
> >>>>> patchers - it's to make life easier for people who actually spend
> >>>>> time debugging the code. And the people who need the debug code
> >>>>> are expected to understand why an ASSERT is not necessary. :)
> >>>>>
> >>>> Dave, Eric and Ben,
> >>>>
> >>>> This was catched by coverity (CID 102348).
> >>>
> >>> You should have put that in the patch description.
> >>>
> >>> Now I understand why there's been a sudden surge of irrelevant one
> >>> line changes from random people that have never touched XFS before.
> >>>
> >>> <sigh>
> >>>
> >>> Ok, lets churn the code just to shut the stupid checker up. This
> >>> doesn't fix a bug, it doesn't change behaviour, it just makes
> >>> coverity happy. Convert it to the for loop plus ASSERT I mentioned
> >>> in a previous message.
> >>
> >> You know, I respectfully disagree, but we might just have to agree
> >> to disagree.  The code, as it stands, tests for a null ptr
> >> and then dereferences it.  That's always going to raise some
> >> eyebrows, coverity or not, debug code or not, drive by or not.
> > 
> >> So even for future developers, making the code more self-
> >> documenting about this behavior would be a plus, whether it's by
> >> comment, by explicit ASSERT(), or whatever.  (I don't think
> >> that xfs_emerg() has quite enough context to make it obvious.)
> > 
> > Sure, but if weren't for the fact that Coverity warned about it,
> > nobody other that us people who work on the XFS code day in, day out
> > would have even cared about it.
> > 
> > That's kind of my point - again, as the Devil's Advocate - that
> > coverity is encouraging drive-by "fixes" by people who don't
> > actually understand any of the context, history and/or culture
> > surrounding the code being modified.
> 
> They shouldn't have to, the code (or comments therein) should
> make it obvious.  ;)  (in a perfect world...)

Obvious to whom, exactly?

That's the point I'm trying to make - "#ifdef DEBUG", two
comments indicating that it's validating the list and printing a
message just before it goes boom. That's pretty obvious code to
anyone who is used to tracking down corrupted list problems...

> > I have no problems with real bugs being fixed, but if we are
> > modifying code for no gain other than closing "coverity doesn't like
> > it" bugs, then we *should* be questioning whether the change is
> > really necessary.
> 
> But let's give Geyslan the benefit of the doubt, and realize that
> Coverity does find real things, and even if it originated w/ a
> Coverity CID, when one sees:
> 
> 	if (!a)
> 		printk("a thing\n")
> 
> 	a = a->b = . . . 
> 
> it looks suspicious to pretty much anyone.  I don't think Geyslan
> sent it to shut Coverity up, he sent it because it looked like
> a bug worth fixing (after Coverity spotted it).
> 
> Let's not be too hard on him for trying; I appreciate it more
> than spelling fixes and whitespace cleanups.  ;)

True, point taken. 

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/