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Diffstat (limited to 'Documentation/process/handling-regressions.rst')
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1 files changed, 151 insertions, 101 deletions
diff --git a/Documentation/process/handling-regressions.rst b/Documentation/process/handling-regressions.rst index abb741b1aeee..1f5ab49c48a4 100644 --- a/Documentation/process/handling-regressions.rst +++ b/Documentation/process/handling-regressions.rst @@ -27,11 +27,11 @@ The important bits (aka "The TL;DR") 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 + 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 + #regzbot ^introduced: 1f2e3d4c5b6a * When forwarding reports from a bug tracker to the regressions list (see above), include a paragraph like the following:: @@ -40,10 +40,13 @@ The important bits (aka "The TL;DR") #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 +#. When submitting fixes for regressions, add "Closes:" 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>`. + :ref:`Documentation/process/5.Posting.rst <development_posting>`. If you are + only fixing part of the issue that caused the regression, you may use + "Link:" tags instead. regzbot currently makes no distinction between the + two. #. 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 @@ -79,7 +82,7 @@ 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 + ``#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 @@ -91,10 +94,10 @@ When doing either, consider making the Linux kernel regression tracking bot 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 + for patches with "Closes:" tags pointing to the report in the archives on lore.kernel.org. - * When forwarding a regressions reported to a bug tracker, include a paragraph + * When forwarding a regression reported to a bug tracker, include a paragraph with these regzbot commands:: #regzbot introduced: 1f2e3d4c5b6a @@ -102,7 +105,7 @@ When doing either, consider making the Linux kernel regression tracking bot #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. + contain "Closes:" tags pointing to your mail or the mentioned ticket. What's important when fixing regressions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -112,10 +115,14 @@ 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:: + * Point to all places where the issue was reported using "Closes:" tags:: - Link: https://lore.kernel.org/r/30th.anniversary.repost@klaava.Helsinki.FI/ - Link: https://bugzilla.kernel.org/show_bug.cgi?id=1234567890 + Closes: https://lore.kernel.org/r/30th.anniversary.repost@klaava.Helsinki.FI/ + Closes: https://bugzilla.kernel.org/show_bug.cgi?id=1234567890 + + If you are only fixing part of the issue, you may use "Link:" instead as + described in the first document mentioned above. regzbot currently treats + both of these equivalently and considers the linked reports as resolved. * Add a "Fixes:" tag to specify the commit causing the regression. @@ -126,91 +133,135 @@ 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 +these tools is regzbot, which heavily relies on the "Closes:" 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. +Expectations and best practices for fixing regressions +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +As a Linux kernel developer, you are expected to give your best to prevent +situations where a regression caused by a recent change of yours leaves users +only these options: + + * Run a kernel with a regression that impacts usage. + + * Switch to an older or newer kernel series. + + * Continue running an outdated and thus potentially insecure kernel for more + than three weeks after the regression's culprit was identified. Ideally it + should be less than two. And it ought to be just a few days, if the issue is + severe or affects many users -- either in general or in prevalent + environments. + +How to realize that in practice depends on various factors. Use the following +rules of thumb as a guide. + +In general: + + * Prioritize work on regressions over all other Linux kernel work, unless the + latter concerns a severe issue (e.g. acute security vulnerability, data loss, + bricked hardware, ...). + + * Expedite fixing mainline regressions that recently made it into a proper + mainline, stable, or longterm release (either directly or via backport). + + * Do not consider regressions from the current cycle as something that can wait + till the end of the cycle, as the issue might discourage or prevent users and + CI systems from testing mainline now or generally. + + * Work with the required care to avoid additional or bigger damage, even if + resolving an issue then might take longer than outlined below. + +On timing once the culprit of a regression is known: + + * Aim to mainline a fix within two or three days, if the issue is severe or + bothering many users -- either in general or in prevalent conditions like a + particular hardware environment, distribution, or stable/longterm series. + + * Aim to mainline a fix by Sunday after the next, if the culprit made it + into a recent mainline, stable, or longterm release (either directly or via + backport); if the culprit became known early during a week and is simple to + resolve, try to mainline the fix within the same week. + + * For other regressions, aim to mainline fixes before the hindmost Sunday + within the next three weeks. One or two Sundays later are acceptable, if the + regression is something people can live with easily for a while -- like a + mild performance regression. + + * It's strongly discouraged to delay mainlining regression fixes till the next + merge window, except when the fix is extraordinarily risky or when the + culprit was mainlined more than a year ago. + +On procedure: + + * Always consider reverting the culprit, as it's often the quickest and least + dangerous way to fix a regression. Don't worry about mainlining a fixed + variant later: that should be straight-forward, as most of the code went + through review once already. + + * Try to resolve any regressions introduced in mainline during the past + twelve months before the current development cycle ends: Linus wants such + regressions to be handled like those from the current cycle, unless fixing + bears unusual risks. + + * Consider CCing Linus on discussions or patch review, if a regression seems + tangly. Do the same in precarious or urgent cases -- especially if the + subsystem maintainer might be unavailable. Also CC the stable team, when you + know such a regression made it into a mainline, stable, or longterm release. + + * For urgent regressions, consider asking Linus to pick up the fix straight + from the mailing list: he is totally fine with that for uncontroversial + fixes. Ideally though such requests should happen in accordance with the + subsystem maintainers or come directly from them. + + * In case you are unsure if a fix is worth the risk applying just days before + a new mainline release, send Linus a mail with the usual lists and people in + CC; in it, summarize the situation while asking him to consider picking up + the fix straight from the list. He then himself can make the call and when + needed even postpone the release. Such requests again should ideally happen + in accordance with the subsystem maintainers or come directly from them. + +Regarding stable and longterm kernels: + + * You are free to leave regressions to the stable team, if they at no point in + time occurred with mainline or were fixed there already. + + * If a regression made it into a proper mainline release during the past + twelve months, ensure to tag the fix with "Cc: stable@vger.kernel.org", as a + "Fixes:" tag alone does not guarantee a backport. Please add the same tag, + in case you know the culprit was backported to stable or longterm kernels. + + * When receiving reports about regressions in recent stable or longterm kernel + series, please evaluate at least briefly if the issue might happen in current + mainline as well -- and if that seems likely, take hold of the report. If in + doubt, ask the reporter to check mainline. + + * Whenever you want to swiftly resolve a regression that recently also made it + into a proper mainline, stable, or longterm release, fix it quickly in + mainline; when appropriate thus involve Linus to fast-track the fix (see + above). That's because the stable team normally does neither revert nor fix + any changes that cause the same problems in mainline. + + * In case of urgent regression fixes you might want to ensure prompt + backporting by dropping the stable team a note once the fix was mainlined; + this is especially advisable during merge windows and shortly thereafter, as + the fix otherwise might land at the end of a huge patch queue. + +On patch flow: + + * Developers, when trying to reach the time periods mentioned above, remember + to account for the time it takes to get fixes tested, reviewed, and merged by + Linus, ideally with them being in linux-next at least briefly. Hence, if a + fix is urgent, make it obvious to ensure others handle it appropriately. + + * Reviewers, you are kindly asked to assist developers in reaching the time + periods mentioned above by reviewing regression fixes in a timely manner. + + * Subsystem maintainers, you likewise are encouraged to expedite the handling + of regression fixes. Thus evaluate if skipping linux-next is an option for + the particular fix. Also consider sending git pull requests more often than + usual when needed. And try to avoid holding onto regression fixes over + weekends -- especially when the fix is marked for backporting. More aspects regarding regressions developers should be aware of @@ -240,7 +291,7 @@ 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" + * the purpose of the "no regressions" rule * what issues actually qualify as regression @@ -282,7 +333,7 @@ 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. +with "Closes:" tags; replies to such patch postings are tracked as well. Combined this data provides good insights into the current state of the fixing process. @@ -294,8 +345,7 @@ 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. +links to the patch description pointing to all reports about the issue fixed. Do I have to use regzbot? ~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -354,9 +404,9 @@ 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 +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 +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. @@ -388,7 +438,7 @@ or itself is a reply to that mail: * Mark a regression as fixed by a commit that is heading upstream or already landed:: - #regzbot fixed-by: 1f2e3d4c5d + #regzbot fix: 1f2e3d4c5d * Mark a regression as a duplicate of another one already tracked by regzbot:: |