linux-kernel - Re: bug-introducing patches

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Date:   Wed, 2 May 2018 22:41:56 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Sasha Levin <Alexander.Levin@...rosoft.com>
Cc:     "ksummit-discuss@...ts.linuxfoundation.org" 
        <ksummit-discuss@...ts.linuxfoundation.org>,
        Greg KH <gregkh@...uxfoundation.org>, "w@....eu" <w@....eu>,
        "julia.lawall@...6.fr" <julia.lawall@...6.fr>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: bug-introducing patches

Hi Sasha,

On Wed, May 2, 2018 at 9:51 PM, Sasha Levin
<Alexander.Levin@...rosoft.com> wrote:
> On Wed, May 02, 2018 at 05:32:37PM +0200, Geert Uytterhoeven wrote:
>>On Tue, May 1, 2018 at 6:38 PM, Sasha Levin
>><Alexander.Levin@...rosoft.com> wrote:
>>> Working on AUTOSEL, it became even more obvious to me how difficult it is for a
>>> patch to get a proper review. Maintainers found it difficult to keep up with
>>> the upstream work for their subsystem, and reviewing additional -stable patches
>>> put even more load on them which some suggested would be more than what they
>>> can handle.
>>
>>Thanks for your work!
>>
>>>  - For some reason, the odds of a -rc commit to be targetted for -stable is
>>>    over 20%, while for merge window commits it's about 3%. I can't quite
>>> explain why that happens, but this would suggest that -rc commits end up
>>> hurting -stable pretty badly.
>>
>>Aren't more -rc commits targeted for -stable because they are bugfixes?
>>Ideally, new features are supposed to be merged during the merge window,
>>while -rc commits fix bugs.
>
> new features can only be merged during a merge window, bug fixes can
> be merged at any point.

I wrote "ideally". There's a big difference between theory and practice...

>>So they can be categorized like:
>>  1. Plain -rc commits,
>
> What's this exactly? -rc commits are only supposed to fix bugs.

... hence not all of them are fixes.

Sometimes fast-tracking a new feature or API reduces dependencies for the
next merge window. This is just one example of IMHO valid non-bugfix
-rc commits.

Between v4.17-rc1 and v4.17-rc3, there are 660 non-merge commits, of which
  - 245 carry a Fixes tag,
  - 196 carry a CC stable,
  - 395 contain the string "fix".
(non-mutually exclusive)

That leaves us with 200 commits not falling in the bugfix category.

>>  2. -rc commits fixing a bug:
>>       a. in the same release cycle,
>>       b. in a previous release.
>>
>>2a assumes the bug was backported to -stable, too, doesn't it?
>
> Bug fixes for features introduced in that release cycle won't be
> backported to stable.

They do, if the original commit was introduced during the same cycle and
backported to stable.

>>Do you have statistics for which categories are most buggy?
>
> I haven't broken it down to subsystems for a few reasons:

I didn't mean break down by subsystem, but by category from the list above
(1, 2a, 2b).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds