Re: [MAINTAINERS SUMMIT] [0/4] Common scenario for four proposals regarding regressions

[Thorsten Leemhuis <linux@leemhuis.info>]

On 20.06.24 14:57, James Bottomley wrote:
> On Thu, 2024-06-20 at 12:32 +0200, Thorsten Leemhuis wrote:
>> On 18.06.24 16:43, James Bottomley wrote:
>>> On Thu, 2024-06-13 at 10:22 +0200, Thorsten Leemhuis wrote:
>
>>> However, for obscure drivers and even some more complex
>>> dependencies, the regression sometimes isn't discovered until it
>>> gets into the hands of the wider pool of testers, often via stable.
>>>
>>> This is important, because it emphasizes that zero regressions in
>>> stable is impossible (and thus preventing backporting patches that
>>> cause regressions is also impossible) if stable is the vehicle by
>>> which some regressions are discovered.
>>
>> Of course "Zero regressions in stable is impossible" as we are
>> dealing with software. ;) And of course even with delayed backport
>> for non-urgent fixes some problems would make it through.
>>
>> But right now users testing mainline sometimes hardly have a chance
>> to test and report problems with mainline in time to prevent a
>> backport. Take Linux 6.7.2 (released 2024-01-25 23:58 UTC) with its
>> 640 changes for example, where users had only 4 days to do so, as
>> almost all of its changes had been merged for 6.8-rc1 (2024-01-21
>> 22:23 UTC). FWIW: 200 of those changes were committed to some
>> subsystem git tree during January, 363 during December, 70 during
>> November, and 7 during October.
> 
> I did make this point here:
> 
> https://lore.kernel.org/all/7794a2b09ae4fa73ac35fdaec4858145a665efea.camel@HansenPartnership.com/
> 
> That merge window fixes should be delayed.  Not because I think a
> longer soak in main would allow us to find many more bugs, simply
> because it was causing reports in the merge window that weren't handled
> because people had other things to do.  The reply was that they're
> already doing it

Only for changes picked by autosel afaics, which are delayed for a while
already, yes (not sure, I think that was in place even before the 6.7 days).

But I'm pretty sure it was not autosel that resulted in most of those
backports that went into 6.7.2 due to the lack of "patch autosel"
messags for those changes.

Those changes afaics were mainly patches with a stable tag (about 94
from a quick check) or a Fixes: tag (630); some had both. And those tags
(and not autosel) afaics were the reason for the backports.

> and when I looked, they actually started doing it for
> the 6.9 merge window (so your 6.7 example is probably out of date).

Yes, things looked differently for those releases iirc. We would need to
ask Greg why; but from what I saw it looks a lot like "Greg was on
vacation and/or busy with other stuff" that slightly mixed things up.

>>  But those are different problems.
>> And the situation regarding the first already got somewhat better
>> from what I can see -- among others afaics due to me prodding people
>> when the queue fixes for recent regression for the -next merge
>> window.
> Yes, that's why I was asking for stats on 6.9 and 6.10 where this delay
> policy was apparently in place.

v6.9.2..v6.9.3: 427 changes, all from the 6.10 merge window. From a
rough check if seems 41 of them have a stable tag and 407 a fixes tag
(some both).

6.9.3 was released on "2024-05-30  7:58 UTC", so not even four days
after 6.10-rc1 went out on "2024-05-26 22:31 UTC".

IOW: less patches then in the 6.7.2 case, but eben less time for users
to test mainline, bisect, and report regression to prevent a backport in
time.

Ciao, Thorsten (who prays he did not do something stupid while
generating those numbers)