Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. SPDX-License-Identifier: (GPL-2.0+ OR CC-BY-4.0)
+.. See the bottom of this file for additional redistribution information.
+
+Handling regressions
+++++++++++++++++++++
+
+*We don't cause regressions* -- this document describes what this "first rule of
+Linux kernel development" means in practice for developers. It complements
+Documentation/admin-guide/reporting-regressions.rst, which covers the topic from a
+user's point of view; if you never read that text, go and at least skim over it
+before continuing here.
+
+The important bits (aka "The TL;DR")
+====================================
+
+#. Ensure subscribers of the `regression mailing list <https://lore.kernel.org/regressions/>`_
+   (regressions@lists.linux.dev) quickly become aware of any new regression
+   report:
+
+    * When receiving a mailed report that did not CC the list, bring it into the
+      loop by immediately sending at least a brief "Reply-all" with the list
+      CCed.
+
+    * Forward or bounce any reports submitted in bug trackers to the list.
+
+#. Make the Linux kernel regression tracking bot "regzbot" track the issue (this
+   is optional, but recommended):
+
+    * For mailed reports, check if the reporter included a line like ``#regzbot
+      introduced v5.13..v5.14-rc1``. If not, send a reply (with the regressions
+      list in CC) containing a paragraph like the following, which tells regzbot
+      when the issue started to happen::
+
+       #regzbot ^introduced 1f2e3d4c5b6a
+
+    * When forwarding reports from a bug tracker to the regressions list (see
+      above), include a paragraph like the following::
+
+       #regzbot introduced: v5.13..v5.14-rc1
+       #regzbot from: Some N. Ice Human <some.human@example.com>
+       #regzbot monitor: http://some.bugtracker.example.com/ticket?id=123456789
+
+#. When submitting fixes for regressions, add "Link:" tags to the patch
+   description pointing to all places where the issue was reported, as
+   mandated by Documentation/process/submitting-patches.rst and
+   :ref:`Documentation/process/5.Posting.rst <development_posting>`.
+
+#. Try to fix regressions quickly once the culprit has been identified; fixes
+   for most regressions should be merged within two weeks, but some need to be
+   resolved within two or three days.
+
+
+All the details on Linux kernel regressions relevant for developers
+===================================================================
+
+
+The important basics in more detail
+-----------------------------------
+
+
+What to do when receiving regression reports
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Ensure the Linux kernel's regression tracker and others subscribers of the
+`regression mailing list <https://lore.kernel.org/regressions/>`_
+(regressions@lists.linux.dev) become aware of any newly reported regression:
+
+ * When you receive a report by mail that did not CC the list, immediately bring
+   it into the loop by sending at least a brief "Reply-all" with the list CCed;
+   try to ensure it gets CCed again in case you reply to a reply that omitted
+   the list.
+
+ * If a report submitted in a bug tracker hits your Inbox, forward or bounce it
+   to the list. Consider checking the list archives beforehand, if the reporter
+   already forwarded the report as instructed by
+   Documentation/admin-guide/reporting-issues.rst.
+
+When doing either, consider making the Linux kernel regression tracking bot
+"regzbot" immediately start tracking the issue:
+
+ * For mailed reports, check if the reporter included a "regzbot command" like
+   ``#regzbot introduced 1f2e3d4c5b6a``. If not, send a reply (with the
+   regressions list in CC) with a paragraph like the following:::
+
+       #regzbot ^introduced: v5.13..v5.14-rc1
+
+   This tells regzbot the version range in which the issue started to happen;
+   you can specify a range using commit-ids as well or state a single commit-id
+   in case the reporter bisected the culprit.
+
+   Note the caret (^) before the "introduced": it tells regzbot to treat the
+   parent mail (the one you reply to) as the initial report for the regression
+   you want to see tracked; that's important, as regzbot will later look out
+   for patches with "Link:" tags pointing to the report in the archives on
+   lore.kernel.org.
+
+ * When forwarding a regressions reported to a bug tracker, include a paragraph
+   with these regzbot commands::
+
+       #regzbot introduced: 1f2e3d4c5b6a
+       #regzbot from: Some N. Ice Human <some.human@example.com>
+       #regzbot monitor: http://some.bugtracker.example.com/ticket?id=123456789
+
+   Regzbot will then automatically associate patches with the report that
+   contain "Link:" tags pointing to your mail or the mentioned ticket.
+
+What's important when fixing regressions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+You don't need to do anything special when submitting fixes for regression, just
+remember to do what Documentation/process/submitting-patches.rst,
+:ref:`Documentation/process/5.Posting.rst <development_posting>`, and
+Documentation/process/stable-kernel-rules.rst already explain in more detail:
+
+ * Point to all places where the issue was reported using "Link:" tags::
+
+       Link: https://lore.kernel.org/r/30th.anniversary.repost@klaava.Helsinki.FI/
+       Link: https://bugzilla.kernel.org/show_bug.cgi?id=1234567890
+
+ * Add a "Fixes:" tag to specify the commit causing the regression.
+
+ * If the culprit was merged in an earlier development cycle, explicitly mark
+   the fix for backporting using the ``Cc: stable@vger.kernel.org`` tag.
+
+All this is expected from you and important when it comes to regression, as
+these tags are of great value for everyone (you included) that might be looking
+into the issue weeks, months, or years later. These tags are also crucial for
+tools and scripts used by other kernel developers or Linux distributions; one of
+these tools is regzbot, which heavily relies on the "Link:" tags to associate
+reports for regression with changes resolving them.
+
+Prioritize work on fixing regressions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+You should fix any reported regression as quickly as possible, to provide
+affected users with a solution in a timely manner and prevent more users from
+running into the issue; nevertheless developers need to take enough time and
+care to ensure regression fixes do not cause additional damage.
+
+In the end though, developers should give their best to prevent users from
+running into situations where a regression leaves them only three options: "run
+a kernel with a regression that seriously impacts usage", "continue running an
+outdated and thus potentially insecure kernel version for more than two weeks
+after a regression's culprit was identified", and "downgrade to a still
+supported kernel series that lack required features".
+
+How to realize this depends a lot on the situation. Here are a few rules of
+thumb for you, in order or importance:
+
+ * Prioritize work on handling regression reports and fixing regression over all
+   other Linux kernel work, unless the latter concerns acute security issues or
+   bugs causing data loss or damage.
+
+ * Always consider reverting the culprit commits and reapplying them later
+   together with necessary fixes, as this might be the least dangerous and
+   quickest way to fix a regression.
+
+ * Developers should handle regressions in all supported kernel series, but are
+   free to delegate the work to the stable team, if the issue probably at no
+   point in time occurred with mainline.
+
+ * Try to resolve any regressions introduced in the current development before
+   its end. If you fear a fix might be too risky to apply only days before a new
+   mainline release, let Linus decide: submit the fix separately to him as soon
+   as possible with the explanation of the situation. He then can make a call
+   and postpone the release if necessary, for example if multiple such changes
+   show up in his inbox.
+
+ * Address regressions in stable, longterm, or proper mainline releases with
+   more urgency than regressions in mainline pre-releases. That changes after
+   the release of the fifth pre-release, aka "-rc5": mainline then becomes as
+   important, to ensure all the improvements and fixes are ideally tested
+   together for at least one week before Linus releases a new mainline version.
+
+ * Fix regressions within two or three days, if they are critical for some
+   reason -- for example, if the issue is likely to affect many users of the
+   kernel series in question on all or certain architectures. Note, this
+   includes mainline, as issues like compile errors otherwise might prevent many
+   testers or continuous integration systems from testing the series.
+
+ * Aim to fix regressions within one week after the culprit was identified, if
+   the issue was introduced in either:
+
+    * a recent stable/longterm release
+
+    * the development cycle of the latest proper mainline release
+
+   In the latter case (say Linux v5.14), try to address regressions even
+   quicker, if the stable series for the predecessor (v5.13) will be abandoned
+   soon or already was stamped "End-of-Life" (EOL) -- this usually happens about
+   three to four weeks after a new mainline release.
+
+ * Try to fix all other regressions within two weeks after the culprit was
+   found. Two or three additional weeks are acceptable for performance
+   regressions and other issues which are annoying, but don't prevent anyone
+   from running Linux (unless it's an issue in the current development cycle,
+   as those should ideally be addressed before the release). A few weeks in
+   total are acceptable if a regression can only be fixed with a risky change
+   and at the same time is affecting only a few users; as much time is
+   also okay if the regression is already present in the second newest longterm
+   kernel series.
+
+Note: The aforementioned time frames for resolving regressions are meant to
+include getting the fix tested, reviewed, and merged into mainline, ideally with
+the fix being in linux-next at least briefly. This leads to delays you need to
+account for.
+
+Subsystem maintainers are expected to assist in reaching those periods by doing
+timely reviews and quick handling of accepted patches. They thus might have to
+send git-pull requests earlier or more often than usual; depending on the fix,
+it might even be acceptable to skip testing in linux-next. Especially fixes for
+regressions in stable and longterm kernels need to be handled quickly, as fixes
+need to be merged in mainline before they can be backported to older series.
+
+
+More aspects regarding regressions developers should be aware of
+----------------------------------------------------------------
+
+
+How to deal with changes where a risk of regression is known
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Evaluate how big the risk of regressions is, for example by performing a code
+search in Linux distributions and Git forges. Also consider asking other
+developers or projects likely to be affected to evaluate or even test the
+proposed change; if problems surface, maybe some solution acceptable for all
+can be found.
+
+If the risk of regressions in the end seems to be relatively small, go ahead
+with the change, but let all involved parties know about the risk. Hence, make
+sure your patch description makes this aspect obvious. Once the change is
+merged, tell the Linux kernel's regression tracker and the regressions mailing
+list about the risk, so everyone has the change on the radar in case reports
+trickle in. Depending on the risk, you also might want to ask the subsystem
+maintainer to mention the issue in his mainline pull request.
+
+What else is there to known about regressions?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Check out Documentation/admin-guide/reporting-regressions.rst, it covers a lot
+of other aspects you want might want to be aware of:
+
+ * the purpose of the "no regressions rule"
+
+ * what issues actually qualify as regression
+
+ * who's in charge for finding the root cause of a regression
+
+ * how to handle tricky situations, e.g. when a regression is caused by a
+   security fix or when fixing a regression might cause another one
+
+Whom to ask for advice when it comes to regressions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Send a mail to the regressions mailing list (regressions@lists.linux.dev) while
+CCing the Linux kernel's regression tracker (regressions@leemhuis.info); if the
+issue might better be dealt with in private, feel free to omit the list.
+
+
+More about regression tracking and regzbot
+------------------------------------------
+
+
+Why the Linux kernel has a regression tracker, and why is regzbot used?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Rules like "no regressions" need someone to ensure they are followed, otherwise
+they are broken either accidentally or on purpose. History has shown this to be
+true for the Linux kernel as well. That's why Thorsten Leemhuis volunteered to
+keep an eye on things as the Linux kernel's regression tracker, who's
+occasionally helped by other people. Neither of them are paid to do this,
+that's why regression tracking is done on a best effort basis.
+
+Earlier attempts to manually track regressions have shown it's an exhausting and
+frustrating work, which is why they were abandoned after a while. To prevent
+this from happening again, Thorsten developed regzbot to facilitate the work,
+with the long term goal to automate regression tracking as much as possible for
+everyone involved.
+
+How does regression tracking work with regzbot?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The bot watches for replies to reports of tracked regressions. Additionally,
+it's looking out for posted or committed patches referencing such reports
+with "Link:" tags; replies to such patch postings are tracked as well.
+Combined this data provides good insights into the current state of the fixing
+process.
+
+Regzbot tries to do its job with as little overhead as possible for both
+reporters and developers. In fact, only reporters are burdened with an extra
+duty: they need to tell regzbot about the regression report using the ``#regzbot
+introduced`` command outlined above; if they don't do that, someone else can
+take care of that using ``#regzbot ^introduced``.
+
+For developers there normally is no extra work involved, they just need to make
+sure to do something that was expected long before regzbot came to light: add
+"Link:" tags to the patch description pointing to all reports about the issue
+fixed.
+
+Do I have to use regzbot?
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+It's in the interest of everyone if you do, as kernel maintainers like Linus
+Torvalds partly rely on regzbot's tracking in their work -- for example when
+deciding to release a new version or extend the development phase. For this they
+need to be aware of all unfixed regression; to do that, Linus is known to look
+into the weekly reports sent by regzbot.
+
+Do I have to tell regzbot about every regression I stumble upon?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Ideally yes: we are all humans and easily forget problems when something more
+important unexpectedly comes up -- for example a bigger problem in the Linux
+kernel or something in real life that's keeping us away from keyboards for a
+while. Hence, it's best to tell regzbot about every regression, except when you
+immediately write a fix and commit it to a tree regularly merged to the affected
+kernel series.
+
+How to see which regressions regzbot tracks currently?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Check `regzbot's web-interface <https://linux-regtracking.leemhuis.info/regzbot/>`_
+for the latest info; alternatively, `search for the latest regression report
+<https://lore.kernel.org/lkml/?q=%22Linux+regressions+report%22+f%3Aregzbot>`_,
+which regzbot normally sends out once a week on Sunday evening (UTC), which is a
+few hours before Linus usually publishes new (pre-)releases.
+
+What places is regzbot monitoring?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Regzbot is watching the most important Linux mailing lists as well as the git
+repositories of linux-next, mainline, and stable/longterm.
+
+What kind of issues are supposed to be tracked by regzbot?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The bot is meant to track regressions, hence please don't involve regzbot for
+regular issues. But it's okay for the Linux kernel's regression tracker if you
+use regzbot to track severe issues, like reports about hangs, corrupted data,
+or internal errors (Panic, Oops, BUG(), warning, ...).
+
+Can I add regressions found by CI systems to regzbot's tracking?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Feel free to do so, if the particular regression likely has impact on practical
+use cases and thus might be noticed by users; hence, please don't involve
+regzbot for theoretical regressions unlikely to show themselves in real world
+usage.
+
+How to interact with regzbot?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+By using a 'regzbot command' in a direct or indirect reply to the mail with the
+regression report. These commands need to be in their own paragraph (IOW: they
+need to be separated from the rest of the mail using blank lines).
+
+One such command is ``#regzbot introduced <version or commit>``, which makes
+regzbot consider your mail as a regressions report added to the tracking, as
+already described above; ``#regzbot ^introduced <version or commit>`` is another
+such command, which makes regzbot consider the parent mail as a report for a
+regression which it starts to track.
+
+Once one of those two commands has been utilized, other regzbot commands can be
+used in direct or indirect replies to the report. You can write them below one
+of the `introduced` commands or in replies to the mail that used one of them
+or itself is a reply to that mail:
+
+ * Set or update the title::
+
+       #regzbot title: foo
+
+ * Monitor a discussion or bugzilla.kernel.org ticket where additions aspects of
+   the issue or a fix are discussed -- for example the posting of a patch fixing
+   the regression::
+
+       #regzbot monitor: https://lore.kernel.org/all/30th.anniversary.repost@klaava.Helsinki.FI/
+
+   Monitoring only works for lore.kernel.org and bugzilla.kernel.org; regzbot
+   will consider all messages in that thread or ticket as related to the fixing
+   process.
+
+ * Point to a place with further details of interest, like a mailing list post
+   or a ticket in a bug tracker that are slightly related, but about a different
+   topic::
+
+       #regzbot link: https://bugzilla.kernel.org/show_bug.cgi?id=123456789
+
+ * Mark a regression as fixed by a commit that is heading upstream or already
+   landed::
+
+       #regzbot fixed-by: 1f2e3d4c5d
+
+ * Mark a regression as a duplicate of another one already tracked by regzbot::
+
+       #regzbot dup-of: https://lore.kernel.org/all/30th.anniversary.repost@klaava.Helsinki.FI/
+
+ * Mark a regression as invalid::
+
+       #regzbot invalid: wasn't a regression, problem has always existed
+
+Is there more to tell about regzbot and its commands?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+More detailed and up-to-date information about the Linux
+kernel's regression tracking bot can be found on its
+`project page <https://gitlab.com/knurd42/regzbot>`_, which among others
+contains a `getting started guide <https://gitlab.com/knurd42/regzbot/-/blob/main/docs/getting_started.md>`_
+and `reference documentation <https://gitlab.com/knurd42/regzbot/-/blob/main/docs/reference.md>`_
+which both cover more details than the above section.
+
+Quotes from Linus about regression
+----------------------------------
+
+Find below a few real life examples of how Linus Torvalds expects regressions to
+be handled:
+
+ * From `2017-10-26 (1/2)
+   <https://lore.kernel.org/lkml/CA+55aFwiiQYJ+YoLKCXjN_beDVfu38mg=Ggg5LFOcqHE8Qi7Zw@mail.gmail.com/>`_::
+
+       If you break existing user space setups THAT IS A REGRESSION.
+
+       It's not ok to say "but we'll fix the user space setup".
+
+       Really. NOT OK.
+
+       [...]
+
+       The first rule is:
+
+        - we don't cause regressions
+
+       and the corollary is that when regressions *do* occur, we admit to
+       them and fix them, instead of blaming user space.
+
+       The fact that you have apparently been denying the regression now for
+       three weeks means that I will revert, and I will stop pulling apparmor
+       requests until the people involved understand how kernel development
+       is done.
+
+ * From `2017-10-26 (2/2)
+   <https://lore.kernel.org/lkml/CA+55aFxW7NMAMvYhkvz1UPbUTUJewRt6Yb51QAx5RtrWOwjebg@mail.gmail.com/>`_::
+
+       People should basically always feel like they can update their kernel
+       and simply not have to worry about it.
+
+       I refuse to introduce "you can only update the kernel if you also
+       update that other program" kind of limitations. If the kernel used to
+       work for you, the rule is that it continues to work for you.
+
+       There have been exceptions, but they are few and far between, and they
+       generally have some major and fundamental reasons for having happened,
+       that were basically entirely unavoidable, and people _tried_hard_ to
+       avoid them. Maybe we can't practically support the hardware any more
+       after it is decades old and nobody uses it with modern kernels any
+       more. Maybe there's a serious security issue with how we did things,
+       and people actually depended on that fundamentally broken model. Maybe
+       there was some fundamental other breakage that just _had_ to have a
+       flag day for very core and fundamental reasons.
+
+       And notice that this is very much about *breaking* peoples environments.
+
+       Behavioral changes happen, and maybe we don't even support some
+       feature any more. There's a number of fields in /proc/<pid>/stat that
+       are printed out as zeroes, simply because they don't even *exist* in
+       the kernel any more, or because showing them was a mistake (typically
+       an information leak). But the numbers got replaced by zeroes, so that
+       the code that used to parse the fields still works. The user might not
+       see everything they used to see, and so behavior is clearly different,
+       but things still _work_, even if they might no longer show sensitive
+       (or no longer relevant) information.
+
+       But if something actually breaks, then the change must get fixed or
+       reverted. And it gets fixed in the *kernel*. Not by saying "well, fix
+       your user space then". It was a kernel change that exposed the
+       problem, it needs to be the kernel that corrects for it, because we
+       have a "upgrade in place" model. We don't have a "upgrade with new
+       user space".
+
+       And I seriously will refuse to take code from people who do not
+       understand and honor this very simple rule.
+
+       This rule is also not going to change.
+
+       And yes, I realize that the kernel is "special" in this respect. I'm
+       proud of it.
+
+       I have seen, and can point to, lots of projects that go "We need to
+       break that use case in order to make progress" or "you relied on
+       undocumented behavior, it sucks to be you" or "there's a better way to
+       do what you want to do, and you have to change to that new better
+       way", and I simply don't think that's acceptable outside of very early
+       alpha releases that have experimental users that know what they signed
+       up for. The kernel hasn't been in that situation for the last two
+       decades.
+
+       We do API breakage _inside_ the kernel all the time. We will fix
+       internal problems by saying "you now need to do XYZ", but then it's
+       about internal kernel API's, and the people who do that then also
+       obviously have to fix up all the in-kernel users of that API. Nobody
+       can say "I now broke the API you used, and now _you_ need to fix it
+       up". Whoever broke something gets to fix it too.
+
+       And we simply do not break user space.
+
+ * From `2020-05-21
+   <https://lore.kernel.org/all/CAHk-=wiVi7mSrsMP=fLXQrXK_UimybW=ziLOwSzFTtoXUacWVQ@mail.gmail.com/>`_::
+
+       The rules about regressions have never been about any kind of
+       documented behavior, or where the code lives.
+
+       The rules about regressions are always about "breaks user workflow".
+
+       Users are literally the _only_ thing that matters.
+
+       No amount of "you shouldn't have used this" or "that behavior was
+       undefined, it's your own fault your app broke" or "that used to work
+       simply because of a kernel bug" is at all relevant.
+
+       Now, reality is never entirely black-and-white. So we've had things
+       like "serious security issue" etc that just forces us to make changes
+       that may break user space. But even then the rule is that we don't
+       really have other options that would allow things to continue.
+
+       And obviously, if users take years to even notice that something
+       broke, or if we have sane ways to work around the breakage that
+       doesn't make for too much trouble for users (ie "ok, there are a
+       handful of users, and they can use a kernel command line to work
+       around it" kind of things) we've also been a bit less strict.
+
+       But no, "that was documented to be broken" (whether it's because the
+       code was in staging or because the man-page said something else) is
+       irrelevant. If staging code is so useful that people end up using it,
+       that means that it's basically regular kernel code with a flag saying
+       "please clean this up".
+
+       The other side of the coin is that people who talk about "API
+       stability" are entirely wrong. API's don't matter either. You can make
+       any changes to an API you like - as long as nobody notices.
+
+       Again, the regression rule is not about documentation, not about
+       API's, and not about the phase of the moon.
+
+       It's entirely about "we caused problems for user space that used to work".
+
+ * From `2017-11-05
+   <https://lore.kernel.org/all/CA+55aFzUvbGjD8nQ-+3oiMBx14c_6zOj2n7KLN3UsJ-qsd4Dcw@mail.gmail.com/>`_::
+
+       And our regression rule has never been "behavior doesn't change".
+       That would mean that we could never make any changes at all.
+
+       For example, we do things like add new error handling etc all the
+       time, which we then sometimes even add tests for in our kselftest
+       directory.
+
+       So clearly behavior changes all the time and we don't consider that a
+       regression per se.
+
+       The rule for a regression for the kernel is that some real user
+       workflow breaks. Not some test. Not a "look, I used to be able to do
+       X, now I can't".
+
+ * From `2018-08-03
+   <https://lore.kernel.org/all/CA+55aFwWZX=CXmWDTkDGb36kf12XmTehmQjbiMPCqCRG2hi9kw@mail.gmail.com/>`_::
+
+       YOU ARE MISSING THE #1 KERNEL RULE.
+
+       We do not regress, and we do not regress exactly because your are 100% wrong.
+
+       And the reason you state for your opinion is in fact exactly *WHY* you
+       are wrong.
+
+       Your "good reasons" are pure and utter garbage.
+
+       The whole point of "we do not regress" is so that people can upgrade
+       the kernel and never have to worry about it.
+
+       > Kernel had a bug which has been fixed
+
+       That is *ENTIRELY* immaterial.
+
+       Guys, whether something was buggy or not DOES NOT MATTER.
+
+       Why?
+
+       Bugs happen. That's a fact of life. Arguing that "we had to break
+       something because we were fixing a bug" is completely insane. We fix
+       tens of bugs every single day, thinking that "fixing a bug" means that
+       we can break something is simply NOT TRUE.
+
+       So bugs simply aren't even relevant to the discussion. They happen,
+       they get found, they get fixed, and it has nothing to do with "we
+       break users".
+
+       Because the only thing that matters IS THE USER.
+
+       How hard is that to understand?
+
+       Anybody who uses "but it was buggy" as an argument is entirely missing
+       the point. As far as the USER was concerned, it wasn't buggy - it
+       worked for him/her.
+
+       Maybe it worked *because* the user had taken the bug into account,
+       maybe it worked because the user didn't notice - again, it doesn't
+       matter. It worked for the user.
+
+       Breaking a user workflow for a "bug" is absolutely the WORST reason
+       for breakage you can imagine.
+
+       It's basically saying "I took something that worked, and I broke it,
+       but now it's better". Do you not see how f*cking insane that statement
+       is?
+
+       And without users, your program is not a program, it's a pointless
+       piece of code that you might as well throw away.
+
+       Seriously. This is *why* the #1 rule for kernel development is "we
+       don't break users". Because "I fixed a bug" is absolutely NOT AN
+       ARGUMENT if that bug fix broke a user setup. You actually introduced a
+       MUCH BIGGER bug by "fixing" something that the user clearly didn't
+       even care about.
+
+       And dammit, we upgrade the kernel ALL THE TIME without upgrading any
+       other programs at all. It is absolutely required, because flag-days
+       and dependencies are horribly bad.
+
+       And it is also required simply because I as a kernel developer do not
+       upgrade random other tools that I don't even care about as I develop
+       the kernel, and I want any of my users to feel safe doing the same
+       time.
+
+       So no. Your rule is COMPLETELY wrong. If you cannot upgrade a kernel
+       without upgrading some other random binary, then we have a problem.
+
+ * From `2021-06-05
+   <https://lore.kernel.org/all/CAHk-=wiUVqHN76YUwhkjZzwTdjMMJf_zN4+u7vEJjmEGh3recw@mail.gmail.com/>`_::
+
+       THERE ARE NO VALID ARGUMENTS FOR REGRESSIONS.
+
+       Honestly, security people need to understand that "not working" is not
+       a success case of security. It's a failure case.
+
+       Yes, "not working" may be secure. But security in that case is *pointless*.
+
+ * From `2011-05-06 (1/3)
+   <https://lore.kernel.org/all/BANLkTim9YvResB+PwRp7QTK-a5VNg2PvmQ@mail.gmail.com/>`_::
+
+       Binary compatibility is more important.
+
+       And if binaries don't use the interface to parse the format (or just
+       parse it wrongly - see the fairly recent example of adding uuid's to
+       /proc/self/mountinfo), then it's a regression.
+
+       And regressions get reverted, unless there are security issues or
+       similar that makes us go "Oh Gods, we really have to break things".
+
+       I don't understand why this simple logic is so hard for some kernel
+       developers to understand. Reality matters. Your personal wishes matter
+       NOT AT ALL.
+
+       If you made an interface that can be used without parsing the
+       interface description, then we're stuck with the interface. Theory
+       simply doesn't matter.
+
+       You could help fix the tools, and try to avoid the compatibility
+       issues that way. There aren't that many of them.
+
+   From `2011-05-06 (2/3)
+   <https://lore.kernel.org/all/BANLkTi=KVXjKR82sqsz4gwjr+E0vtqCmvA@mail.gmail.com/>`_::
+
+       it's clearly NOT an internal tracepoint. By definition. It's being
+       used by powertop.
+
+   From `2011-05-06 (3/3)
+   <https://lore.kernel.org/all/BANLkTinazaXRdGovYL7rRVp+j6HbJ7pzhg@mail.gmail.com/>`_::
+
+       We have programs that use that ABI and thus it's a regression if they break.
+
+ * From `2012-07-06 <https://lore.kernel.org/all/CA+55aFwnLJ+0sjx92EGREGTWOx84wwKaraSzpTNJwPVV8edw8g@mail.gmail.com/>`_::
+
+       > Now this got me wondering if Debian _unstable_ actually qualifies as a
+       > standard distro userspace.
+
+       Oh, if the kernel breaks some standard user space, that counts. Tons
+       of people run Debian unstable
+
+ * From `2019-09-15
+   <https://lore.kernel.org/lkml/CAHk-=wiP4K8DRJWsCo=20hn_6054xBamGKF2kPgUzpB5aMaofA@mail.gmail.com/>`_::
+
+       One _particularly_ last-minute revert is the top-most commit (ignoring
+       the version change itself) done just before the release, and while
+       it's very annoying, it's perhaps also instructive.
+
+       What's instructive about it is that I reverted a commit that wasn't
+       actually buggy. In fact, it was doing exactly what it set out to do,
+       and did it very well. In fact it did it _so_ well that the much
+       improved IO patterns it caused then ended up revealing a user-visible
+       regression due to a real bug in a completely unrelated area.
+
+       The actual details of that regression are not the reason I point that
+       revert out as instructive, though. It's more that it's an instructive
+       example of what counts as a regression, and what the whole "no
+       regressions" kernel rule means. The reverted commit didn't change any
+       API's, and it didn't introduce any new bugs. But it ended up exposing
+       another problem, and as such caused a kernel upgrade to fail for a
+       user. So it got reverted.
+
+       The point here being that we revert based on user-reported _behavior_,
+       not based on some "it changes the ABI" or "it caused a bug" concept.
+       The problem was really pre-existing, and it just didn't happen to
+       trigger before. The better IO patterns introduced by the change just
+       happened to expose an old bug, and people had grown to depend on the
+       previously benign behavior of that old issue.
+
+       And never fear, we'll re-introduce the fix that improved on the IO
+       patterns once we've decided just how to handle the fact that we had a
+       bad interaction with an interface that people had then just happened
+       to rely on incidental behavior for before. It's just that we'll have
+       to hash through how to do that (there are no less than three different
+       patches by three different developers being discussed, and there might
+       be more coming...). In the meantime, I reverted the thing that exposed
+       the problem to users for this release, even if I hope it will be
+       re-introduced (perhaps even backported as a stable patch) once we have
+       consensus about the issue it exposed.
+
+       Take-away from the whole thing: it's not about whether you change the
+       kernel-userspace ABI, or fix a bug, or about whether the old code
+       "should never have worked in the first place". It's about whether
+       something breaks existing users' workflow.
+
+       Anyway, that was my little aside on the whole regression thing.  Since
+       it's that "first rule of kernel programming", I felt it is perhaps
+       worth just bringing it up every once in a while
+
+..
+   end-of-content
+..
+   This text is available under GPL-2.0+ or CC-BY-4.0, as stated at the top
+   of the file. If you want to distribute this text under CC-BY-4.0 only,
+   please use "The Linux kernel developers" for author attribution and link
+   this as source:
+   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Documentation/process/handling-regressions.rst
+..
+   Note: Only the content of this RST file as found in the Linux kernel sources
+   is available under CC-BY-4.0, as versions of this text that were processed
+   (for example by the kernel's build system) might contain content taken from
+   files which use a more restrictive license.