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Date: Thu, 18 Apr 2024 13:53:10 +0300
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Ricardo Ribalda <ribalda@chromium.org>
Cc: Dan Carpenter <dan.carpenter@linaro.org>,
	Martin Tuma <martin.tuma@digiteqautomotive.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
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	Sakari Ailus <sakari.ailus@linux.intel.com>,
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	Oleg Drokin <green@linuxhacker.ru>
Subject: Re: [PATCH 00/35] media: Fix coccinelle warning/errors
Message-ID: <20240418105310.GV12561@pendragon.ideasonboard.com>
References: <20240415-fix-cocci-v1-0-477afb23728b@chromium.org>
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In-Reply-To: <CANiDSCs_qOXkhzuL+cFhpw0hvFMwU0TYyN2B5ZdAStb96TTKFA@mail.gmail.com>

Hi Ricardo,

On Wed, Apr 17, 2024 at 06:19:14PM +0200, Ricardo Ribalda wrote:
> On Wed, 17 Apr 2024 at 17:51, Laurent Pinchart wrote:
> > On Tue, Apr 16, 2024 at 11:47:17AM +0300, Dan Carpenter wrote:
> > > In my opinion, it's better to just ignore old warnings.
> >
> > I agree. Whatever checkers we enable, whatever code we test, there will
> > always be false positives. A CI system needs to be able to ignore those
> > false positives and only warn about new issues.
> 
> We already have support for that:
> https://gitlab.freedesktop.org/linux-media/media-ci/-/tree/main/testdata/static?ref_type=heads

Those are manually written filters. Would it be possible to reduce the
manual step to flagging something as a false positive, and have a
machine build the filters ?

> But it would be great if those lists were as small as possible:
> 
> - If we have a lot of warnings, two error messages can be combined and
> will scape the filters
> eg:
> print(AAAA);
> print(BBBB);
> > AABBBAAB
> 
> - The filters might hide new errors if they are too broad
> 
> 
> Most of the patches in this series are simple and make a nicer code:
> Eg the non return minmax() ,
> Other patches show real integer overflows.
> 
> Now that the patches are ready, let's bite the bullet and try to
> reduce our technical debt.
> 
> > > When code is new the warnings are going to be mostly correct.  The
> > > original author is there and knows what the code does.  Someone has
> > > the hardware ready to test any changes.  High value, low burden.
> > >
> > > When the code is old only the false positives are left.  No one is
> > > testing the code.  It's low value, high burden.
> > >
> > > Plus it puts static checker authors in a difficult place because now
> > > people have to work around our mistakes.  It creates animosity.
> > >
> > > Now we have to hold ourselves to a much higher standard for false
> > > positives.  It sounds like I'm complaining and lazy, right?  But Oleg
> > > Drokin has told me previously that I spend too much time trying to
> > > silence false positives instead of working on new code.  He's has a
> > > point which is that actually we have limited amount of time and we have
> > > to make choices about what's the most useful thing we can do.
> > >
> > > So what I do and what the zero day bot does is we look at warnings one
> > > time and we re-review old warnings whenever a file is changed.
> > >
> > > Kernel developers are very good at addressing static checker warnings
> > > and fixing the real issues...  People sometimes ask me to create a
> > > database of warnings which I have reviewed but the answer is that
> > > anything old can be ignored.  As I write this, I've had a thought that
> > > instead of a database of false positives maybe we should record a
> > > database of real bugs to ensure that the fixes for anything real is
> > > applied.

-- 
Regards,

Laurent Pinchart