Re: [MAINTAINERS SUMMIT] [4/4] Discuss how to better prevent backports of commits that turn out to cause regressions

Jan Kara
2024-06-13T09:59:20Z

On Thu 13-06-24 10:42:01, Thorsten Leemhuis wrote:
> * One cause of regressions that happen in stable trees (and not in
> mainline) I've seen quite a few times are backports of commits with
> Fixes: tags that were part of a patch-series and depend on earlier
> patches from the series. The stable-team afaics has no easy way to spot
> this, as there is no way to check "was this change part of a series".
> Sometimes I wonder if a dedicated tag linking to the submission of a
> patch could help -- and is something quite a few maintainers already
> really want and add using a "Link" tag despite Linus dislike for that
> (IIRC).

FWIW I (and a few other maintainers) use 'Message-Id' tag to link to
submission. This is still easily convertible to lore link and unlike 'Link'
tag it is clear what this tag is about and that it is not just a link to
related discussion or something like that. AFAIK this also addresses Linus'
dislike because what he was complaining about is that 'Link' should be
linking to some useful context for the changelog, not just patch
submission.

> But following that link for each and every patch slated for
> backporting does not scale for the stable team anyway, so it's likely
> not worth it.

Well, what I'd propose is that if 'Message-Id' tag is present and thus it
can be established (in an automated way using lore) which series this patch
was part of, then stable maintainers will either pick all patches from the
start of the series upto this change or nothing. Because what I see
happening several times in a year just in subsystems I maintain is that
stable tree picks up more or less random subset of a patch series
(depending on what applies and what their algorithms decide to take) and
that causes issues. Sometimes we catch that during glancing over patches
flowing into stable (like Amir did last week) but sometimes we don't and
breakage happens.

This will require a bit more discipline when creating patch series to put
more or less independent fixes that should go into stable first but that is
a good practice anyway and mostly followed at least in the areas of the
kernel I work in.

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR