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| -rw-r--r-- | Documentation/process/handling-regressions.rst | 87 |
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diff --git a/Documentation/process/handling-regressions.rst b/Documentation/process/handling-regressions.rst index e1102a3207e3..abb741b1aeee 100644 --- a/Documentation/process/handling-regressions.rst +++ b/Documentation/process/handling-regressions.rst @@ -45,6 +45,10 @@ The important bits (aka "The TL;DR") 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 =================================================================== @@ -125,6 +129,89 @@ 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leaves them only three options: "run +a kernel with a regression that seriously impacts usage", "continue running an +outdated and thus potentially insecure kernel version for more than two weeks +after a regression's culprit was identified", and "downgrade to a still +supported kernel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 ---------------------------------------------------------------- |