Stable derivative branch handling

[Andy Whitcroft]

[This email is the result of a number of IRC conversations and chats
about derivative branch handing, particularly focused on ensuring that
we are maintaining forward progress on CVEs for all supported branches.]

The stable team has repsonsibilty for preparation of the master distro
kernels, uploading them, and shepherding them through the phases of the
stable cadance in a timely fashion.

>From a kernel maintenance point of view this has meant that the greater
team has continued to review updates and apply those to the pending
branches (master-next et al).  The stable team has then taken the current
contents of those pending branches and rolled those up and pushed them
onto the cadance conveyor.

Derivative branches have typically been rebased by the stable team where
that is successful with those being pushed to a domain expert on failure.
Typically such failures have not held up the cadance.

After some discussion on IRC it was decided that it is time we formalised
the process for derivative branches and the interactions between the core
team and the domain experts for preparing kernels for release, such that we
have formal checkpoints in the stable cadance to ensure that the derivative
branches are updated when required but do not prevent forward progress.

To this end once the main distro kernel tree are prepared the kernel
stable team will announce their availability to the derivative branch
maintainers.  This will indicate that the master branches are now ready
for rebasing onto where that is appropriate.  The derivative maintainers
will then rebase if required and determine if their branch has anything
worthy of an upload.  If so they will reply to the announcement adding
their branch to the versions to pushed this cycle.  The stable team will
then handle closing and uploading this branch with the main branches.
If the derivative branches are not ready in time for upload, they will
simply slip to the next cadance round.

The current derivative branch maintainers are:

 - smb: Lucid -ec2
 - ppisati: everything arm

Comments?

-apw