Re: How to improve the quality of the kernel?

Michal Piotrowski
2007-06-17T18:54:45Z

On 17/06/07, Bartlomiej Zolnierkiewicz <bzolnier@gmail.com> wrote:
>
> Hi,
>
> On Sunday 17 June 2007, Adrian Bunk wrote:
> > On Sun, Jun 17, 2007 at 03:17:58PM +0200, Michal Piotrowski wrote:
> > > On 17/06/07, Adrian Bunk <bunk@stusta.de> wrote:
> > >...
> > >> Fine with me, but:
> > >>
> > >> There are not so simple cases like big infrastructure patches with
> > >> 20 other patches in the tree depending on it causing a regression, or
> > >> even worse, a big infrastructure patch exposing a latent old bug in some
> > >> completely different area of the kernel.
> > >
> > > It is different case.
> > >
> > > "If the patch introduces a new regression"
> > >
> > > introduces != exposes an old bug
> >
> > My remark was meant as a note "this sentence can't handle all
> > regressions" (and for a user it doesn't matter whether a new
> > regression is introduced or an old regression exposed).
> >
> > It could be we simply agree on this one. ;-)
> >
> > > Removal of 20 patches will be painful, but sometimes you need to
> > > "choose minor evil to prevent a greater one" [1].
> > >
> > >> And we should be aware that reverting is only a workaround for the real
> > >> problem which lies in our bug handling.
> > >...
> >
> > And this is something I want to emphasize again.
> >
> > How can we make any progress with the real problem and not only the
> > symptoms?
> >
> > There's now much money in the Linux market, and the kernel quality
> > problems might result in real costs in the support of companies like
> > IBM, SGI, Redhat or Novell (plus it harms the Linux image which might
> > result in lower revenues).
> >
> > If [1] this is true, it might even pay pay off for them to each assign
> > X man hours per month of experienced kernel developers to upstream
> > kernel bug handling?
> >
> > This is just a wild thought and it might be nonsense - better
> > suggestions for solving our quality problems would be highly welcome...
>
> IMO we should concentrate more on preventing regressions than on fixing them.
> In the long-term preventing bugs is cheaper than fixing them afterwards.
>
> First let me tell you all a little story...
>
> Over two years ago I've reviewed some _cleanup_ patch and noticed three bugs
> in it (in other words I potentially prevented three regressions). I also
> asked for more thorough verification of the patch as I suspected that it may
> have more problems. The author fixed the issues and replied that he hasn't
> done the full verification yet but he doesn't suspect any problems...
>
> Fast forward...
>
> Year later I discover that the final version of the patch hit the mainline.
> I don't remember ever seeing the final version in my mailbox (there are no
> cc: lines in the patch description) and I saw that I'm not credited in the
> patch description. However the worse part is that it seems that the full
> verification has never been done. The result? Regression in the release
> kernel (exactly the issue that I was worried about) which required three
> patches and over a month to be fixed completely. It seems that a year
> was not enough to get this ~70k _cleanup_ patch fully verified and tested
> (it hit -mm soon before being merged)...
>
> From reviewer's POV: I have invested my time into review, discovered real
> issues and as a reward I got no credit et all and extra frustration from the
> fact that part of my review was forgotten/ignored (the part which resulted in
> real regression in the release kernel)... Oh and in the past the said
> developer has already been asked (politely in private message) to pay more
> attention to his changes (after I silently fixed some other regression caused
> by his other patch).
>
> But wait there is more, I happend to be the maintainer of the subsystem which
> got directly hit by the issue and I was getting bugreports from the users about
> the problem... :-)
>
> It wasn't my first/last bad experience as a reviewer... finally I just gave up
> on reviewing other people patches unless they are stricly for IDE subsystem.
>
> The moral of the story is that currently it just doesn't pay off to do
> code reviews. From personal POV it pays much more to wait until buggy patch
> hits the mainline and then fix the issues yourself (at least you will get
> some credit). To change this we should put more ephasize on the importance
> of code reviews by "rewarding" people investing their time into reviews
> and "rewarding" developers/maintainers taking reviews seriously.
>
> We should credit reviewers more, sometimes it takes more time/knowledge to
> review the patch than to make it so getting near to zero credit for review
> doesn't sound too attractive. Hmm, wait it can be worse - your review
> may be ignored... ;-)
>
> From my side I think I'll start adding less formal "Reviewed-by" to IDE
> patches even if the review resulted in no issues being found (in additon to
> explicit "Acked-by" tags and crediting people for finding real issues - which
> I currently always do as a way for showing my appreciation for their work).
>
> I also encourage other maintainers/developers to pay more attention to
> adding "Acked-by"/"Reviewed-by" tags and crediting reviewers. I hope
> that maintainers will promote changes that have been reviewed by others
> by giving them priority over other ones (if the changes are on more-or-less
> the same importance level of course, you get the idea).

I think that this is a very good idea - especially for large, intrusive patches.
Long {Acked,Reviewed,Signed-off,Tested}-by list will be welcome.

>
> Now what to do with people who ignore reviews and/or have rather high
> regressions/patches ratio?
>
> I think that we should have info about regressions integrated into SCM,
> i.e. in git we should have optional "fixes-commit" tag and we should be
> able to do some reverse data colletion. This feature combined with
> "Author:" info after some time should give us some very interesting
> statistics (Top Ten "Regressors"). It wouldn't be ideal (ie. we need some
> patches threshold to filter out people with 1 patch and >= 1 regression(s),
> we need to remember that some code areas are more difficult than the others
> and that patches are not equal per se etc.) however I believe than making it
> into Top Ten "Regressors" should give the winners some motivation to improve
> their work ethic. Well, in the worst case we would just get some extra
> trivial/documentation patches. ;-)
>
> Sorry for a bit chaotic mail but I hope that message is clear.
>
> Thanks,
> Bart
>

Regards,
Michal

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