docs: *-regressions.rst: Add colon to regzbot commands

Use colon as command terminator everywhere for consistency, even though
it's not strictly necessary. That way it will also match regzbot's
reference documentation.

Link: https://gitlab.com/knurd42/regzbot/-/blob/main/docs/reference.md
Reviewed-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: "Nícolas F. R. A. Prado" <nfraprado@collabora.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20240311-regzbot-fixes-v2-1-98c1b6ec0678@collabora.com>

docs: *-regressions.rst: explain how quickly issues should be handled

Add a section with a few rules of thumb about how
quickly developers should address regressions to
Documentation/process/handling-regressions.rst; additionally,
add a short paragraph about this to the companion document
Documentation/admin-guide/reporting-regressions.rst as well.

The rules of thumb were written after studying the quotes from Linus
found in handling-regressions.rst and especially influenced by
statements like "Users are literally the _only_ thing that matters" and
"without users, your program is not a program, it's a pointless piece of
code that you might as well throw away". The author interpreted those in
perspective to how the various Linux kernel series are maintained
currently and what those practices might mean for users running into a
regression on a small or big kernel update.

That for example lead to the paragraph starting with "Aim to get fixes
for regressions mainlined within one week after identifying the culprit,
if the regression was introduced in a stable/longterm release or the
devel cycle for the latest mainline release". Some might see this as
pretty high bar, but on the other hand something like that is needed to
not leave users out in the cold for too long -- which can quickly happen
when updating to the latest stable series, as the previous one is
normally stamped "End of Life" about three or four weeks after a new
mainline release. This makes a lot of users switch during this
timeframe. Any of them thus risk running into regressions not promptly
fixed; even worse, once the previous stable series is EOLed for real,
users that face a regression might be left with only three options:

(1) continue running an outdated and thus potentially insecure kernel
version from an abandoned stable series

(2) run the kernel with the regression

(3) downgrade to an earlier longterm series still supported

This is better avoided, as (1) puts users and their data in danger, (2)
will only be possible if it's a minor regression that doesn't interfere
with booting or serious usage, and (3) might be regression itself or
impossible on the particular machine, as the users might require drivers
or features only introduced after the latest longterm series branched
of.

In the end this lead to the aforementioned "Aim to fix regression within
one week" part. It's also the reason for the "Try to resolve any
regressions introduced in the current development cycle before its
end.".

Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
CC: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/a7b717b52c0d54cdec9b6daf56ed6669feddee2c.1644994117.git.linux@leemhuis.info
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: add two documents about regression handling

Create two documents explaining various aspects around regression
handling and tracking; one is aimed at users, the other targets
developers.

The texts among others describes the first rule of Linux kernel
development and what it means in practice. They also explain what a
regression actually is and how to report one properly.

Both texts additionally provide a brief introduction to the bot the
kernel's regression tracker uses to facilitate the work, but mention the
use is optional.

To sum things up, provide a few quotes from Linus in the document for
developers to show how serious we take regressions.

Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Link: https://lore.kernel.org/r/34e56d3588f22d7e0b4d635ef9c9c3b33ca4ac04.1644994117.git.linux@leemhuis.info
Signed-off-by: Jonathan Corbet <corbet@lwn.net>