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

Sasha Levin
2024-06-13T13:27:55Z

On Thu, Jun 13, 2024 at 07:58:58AM -0400, James Bottomley wrote:
>On Thu, 2024-06-13 at 10:42 +0200, Thorsten Leemhuis wrote:
>> The scenario shown at the start of the thread illustrates a problem I
>> see frequently: commits with a Fixes: tag end up in new to stable
>> series releases just days after being mainlined and cause regressions
>> -- just like they do in mainline, which just was not known yet at the
>> time of backporting. This happens extremely often right after merge
>> windows when huge piles of changes are backported to the stable trees
>> each cycle shortly after -rc1 is out (which even some kernel
>> developers apparently are somewhat afraid to test from what I've
>> seen).
>
>I haven't really observed this for curated fixes. For most subsystems,
>patches with Fixes tags that are cc'd to stable tend to go steadily
>outside the merge window. Obviously a few arrive within it, but
>usually at roughly the rate they arrive outside it.
>
>What I observe in the merge window is huge piles of patches go into
>stable *without* a cc:stable tag from the autosel machinery (and quite
>a few even without fixes: tags).

Could you provide a concrete example? This shouldn't happen.

>So this does beg a couple of questions:
>
>Since you have the figures, what's the proportion of regressions caused
>by backports to stable without cc:stable tags?

This question came up two years ago and we had statistics around this.
Autosel patches didn't cause more (actually, it was *less*) regressions
than stable tagged ones.

>Could we fix a lot of this by delaying autosel? It tends to ramp up in
>the merge window when everyone is concentrating on other things, so any
>regressions it causes naturally get ignored for a couple of weeks.

autosel is currently delayed about 3-4 weeks, sometimes more.

--
Thanks,
Sasha