docs: add two texts covering regressions

"We don't cause regressions" might be the first rule of Linux kernel development, but it and other aspects of regressions nevertheless are hardly described in the Linux kernel's documentation. The following patches change this by creating two documents dedicated to the topic.

The second patch could easily be folded into the first one, but was kept separate, as it might be a bit controversial. This also allows the patch description to explain some backgrounds for this part of the document. Additionally, ACKs and Reviewed-by tags can be collected separately this way.

v5 (this version):
- rename the two documents after review feedback from Jon
- drop the reviewed-by and ACK in the second patch: I slightly changed one entry (the one (the one starting with 'Aim to fix regressions within one week') and added one (the one starting with 'Developers should handle regressions in all supported kernel series') after review feedback from Jon
- remind developers to use "Fixes:" and "Cc: [email protected]" tags in "What's important when fixing regressions"
- drop a few quotes from Linus
- while modifying Documentation/admin-guide/reporting-issues.rst remove quotes around doc references
- a few small adjustments and fixes along the way

v4 (https://lore.kernel.org/lkml/[email protected]/):
- countless small and medium changes after review feedback from Jon (thx), which also lead to a big change:
- split the document into two, one for users and one for developers (both added by the first patch, as they are interlinked).
- fixed and improved a bunch of areas I stumbled upon while checking the text again after the split
- add a third patch to get one of the user-centric document on regressions mentioned in Documentation/admin-guide/reporting-issues.rst
- note: the content added by the second patch did not change significantly, that's why I left an earlier reviewed-by for the patch and an ACK for the series in place there, but dropped the ACK for the first patch of the series

v3 (https://lore.kernel.org/regressions/[email protected]/):
- drop RFC tag
- heavily reshuffled and slightly adjusted the text in the sections "The important bits for people fixing regressions" and "How to add a regression to regzbot's tracking somebody else reported?" to make them easier to grasp
- a few small fixes and improvements
- add ACK for the series from Greg (now for real)

v2/RFC (https://lore.kernel.org/linux-doc/[email protected]/):
- a lot of small fixes, most are for spelling mistakes and grammar errors/problems pointed out in the review feedback I got so far
- add ACK for the series from Greg

v1/RFC (https://lore.kernel.org/linux-doc/[email protected]/):
- initial version

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Hi! Here is the latest version of my patch-set adding documentation regarding regressions. It's mostly fine-tuning after the latest review feedback from Jon.

@Greg, @Linus, would be cool if you could at least take a look at the second patch and ACK or comment on it to make sure the text is really okay for you, now that Jon indicated he's willing to apply this, unless objections show up.

Ciao, Thorsten

Thorsten Leemhuis (3):
docs: add two documents about regression handling
docs: *-regressions.rst: explain how quickly issues should be handled
docs: reporting-issues.rst: link new document about regressions

 Documentation/admin-guide/index.rst           |   1 +
 .../admin-guide/reporting-issues.rst          |  73 +-
 .../admin-guide/reporting-regressions.rst     | 451 +++++++++++
 .../process/handling-regressions.rst          | 746 ++++++++++++++++++
 Documentation/process/index.rst               |   1 +
 MAINTAINERS                                   |   2 +
 6 files changed, 1237 insertions(+), 37 deletions(-)
 create mode 100644 Documentation/admin-guide/reporting-regressions.rst
 create mode 100644 Documentation/process/handling-regressions.rst

base-commit: f647de4b02dcb1815fb3019f86a001a681daf0a1

2.35.1