Patch Propagation

[Seth Forshee]

On Mon, Oct 14, 2019 at 04:08:18AM -0700, MF Ghani wrote:
> Hi,
> What is the current workflow of the patch propagation from linux mainline
> to ubuntu kernel versions? are the downstream ubuntu kernels rebased
> against the latest mainline kernel version? or are they just rebased
> against the mainline kernel version from which a particular ubuntu version
> was initially forked from. e.g is ubuntu 18.04 (bionic) rebased against the
> minor releases of 4.15.x only or are they rebased against the latest
> mainline version lets say 5.0.

Before the final upstream release of a given kernel version the Ubuntu
kernel based on that version will be rebased on each -rc tag. Once the
final upstream release is out, we cherry-pick all patches from the
upstream stable releases into our trees.

The GA kernel for a given release remains on the same kernel version as
at the time of release, e.g. the bionic GA kernel will always be based
on 4.15. We also offer hwe kernels which roll forward to the latest
kernel from a supported Ubuntu release, up to the next LTS release. See
[1] for more information.

> Also, are the latest patches from linux mainline propagated to ubuntu LTS
> versions that are still being supported. if so, what's the process?

We certainly do not backport every patch from mainline, but yes we do
continue to backport patches as needed. There are few primary ways
patches from mainline make their way to Ubuntu kernels:

 1. In response to reported bugs, if a fix is identified upstream we
    will backport the fix. Under some conditions we will also backport
    new features and hardware support.

 2. The upstream stable process. As long as a release is receiving
    stable updates upstream we will continue to apply those. Once a
    release is no longer supported upstream we will use criteria similar
    to upstream stable to identify patches from mainline and backport
    those.

 3. We also monitor all CVEs against the kernel and backport patches as
    appropriate.

Hope that helps,
Seth

[1] https://wiki.ubuntu.com/Kernel/RollingLTSEnablementStack