Everything you ever wanted to know about Linux -stable releases

Rules on what kind of patches are accepted, and which ones are not, into the “-stable” tree:

  • It must be obviously correct and tested.

  • It cannot be bigger than 100 lines, with context.

  • It must fix only one thing.

  • It must fix a real bug that bothers people (not a, “This could be a problem…” type thing).

  • It must fix a problem that causes a build error (but not for things marked CONFIG_BROKEN), an oops, a hang, data corruption, a real security issue, or some “oh, that’s not good” issue. In short, something critical.

  • Serious issues as reported by a user of a distribution kernel may also be considered if they fix a notable performance or interactivity issue. As these fixes are not as obvious and have a higher risk of a subtle regression they should only be submitted by a distribution kernel maintainer and include an addendum linking to a bugzilla entry if it exists and additional information on the user-visible impact.

  • New device IDs and quirks are also accepted.

  • No “theoretical race condition” issues, unless an explanation of how the race can be exploited is also provided.

  • It cannot contain any “trivial” fixes in it (spelling changes, whitespace cleanups, etc).

  • It must follow the Submitting patches: the essential guide to getting your code into the kernel rules.

  • It or an equivalent fix must already exist in Linus’ tree (upstream).

Procedure for submitting patches to the -stable tree

  • Security patches should not be handled (solely) by the -stable review process but should follow the procedures in Security bugs.

For all other submissions, choose one of the following procedures

Option 1

To have the patch automatically included in the stable tree, add the tag

Cc: stable@vger.kernel.org

in the sign-off area. Once the patch is merged it will be applied to the stable tree without anything else needing to be done by the author or subsystem maintainer.

Option 2

After the patch has been merged to Linus’ tree, send an email to stable@vger.kernel.org containing the subject of the patch, the commit ID, why you think it should be applied, and what kernel version you wish it to be applied to.

Option 3

Send the patch, after verifying that it follows the above rules, to stable@vger.kernel.org. You must note the upstream commit ID in the changelog of your submission, as well as the kernel version you wish it to be applied to.

Option 1 is strongly preferred, is the easiest and most common. Option 2 and Option 3 are more useful if the patch isn’t deemed worthy at the time it is applied to a public git tree (for instance, because it deserves more regression testing first). Option 3 is especially useful if the patch needs some special handling to apply to an older kernel (e.g., if API’s have changed in the meantime).

Note that for Option 3, if the patch deviates from the original upstream patch (for example because it had to be backported) this must be very clearly documented and justified in the patch description.

The upstream commit ID must be specified with a separate line above the commit text, like this:

commit <sha1> upstream.

Additionally, some patches submitted via Option 1 may have additional patch prerequisites which can be cherry-picked. This can be specified in the following format in the sign-off area:

Cc: <stable@vger.kernel.org> # 3.3.x: a1f84a3: sched: Check for idle
Cc: <stable@vger.kernel.org> # 3.3.x: 1b9508f: sched: Rate-limit newidle
Cc: <stable@vger.kernel.org> # 3.3.x: fd21073: sched: Fix affinity logic
Cc: <stable@vger.kernel.org> # 3.3.x
Signed-off-by: Ingo Molnar <mingo@elte.hu>

The tag sequence has the meaning of:

git cherry-pick a1f84a3
git cherry-pick 1b9508f
git cherry-pick fd21073
git cherry-pick <this commit>

Also, some patches may have kernel version prerequisites. This can be specified in the following format in the sign-off area:

Cc: <stable@vger.kernel.org> # 3.3.x

The tag has the meaning of:

git cherry-pick <this commit>

For each “-stable” tree starting with the specified version.

Following the submission:

  • The sender will receive an ACK when the patch has been accepted into the queue, or a NAK if the patch is rejected. This response might take a few days, according to the developer’s schedules.

  • If accepted, the patch will be added to the -stable queue, for review by other developers and by the relevant subsystem maintainer.

Review cycle

  • When the -stable maintainers decide for a review cycle, the patches will be sent to the review committee, and the maintainer of the affected area of the patch (unless the submitter is the maintainer of the area) and CC: to the linux-kernel mailing list.

  • The review committee has 48 hours in which to ACK or NAK the patch.

  • If the patch is rejected by a member of the committee, or linux-kernel members object to the patch, bringing up issues that the maintainers and members did not realize, the patch will be dropped from the queue.

  • At the end of the review cycle, the ACKed patches will be added to the latest -stable release, and a new -stable release will happen.

  • Security patches will be accepted into the -stable tree directly from the security kernel team, and not go through the normal review cycle. Contact the kernel security team for more details on this procedure.


Review committee

  • This is made up of a number of kernel developers who have volunteered for this task, and a few that haven’t.