question about one of your ubuntu patch

[Thadeu Lima de Souza Cascardo]

On Tue, Aug 11, 2020 at 12:33:17AM -0700, David Lee wrote:
> Hi,
> 
> I saw your email in the patch "serdev: Fix serdev_uevent failure on ACPI
> enumerated serdev-controllers 586ca5b1a90b66eb0a2805c9419683e33d1d418b" in
> ubuntu's git repository.
> I am surprised to find that this patch in ubuntu git is committed on Apr 12
> 10:06:37 2018. But this patch is committed to linux 4.15 stable branch
> on Apr 12 12:31:11 2018.
> In ubuntu git repository, this patch is also in Linux 4.15 stable branch.
> Why a patch is committed before it's added in Linux 4.15 stable branch?
> 
> Thanks

Hi, David.

There is no upstream Linux 4.15 stable branch. Upstream kernel.org git trees
closest to 4.15 are 4.14 and 4.19. Kamal Mostafa, from the Ubuntu Kernel team
picks up commits from those trees in order to apply them to Ubuntu bionic
kernel tree, which is based on 4.15. As upstream has stopped publishing updates
to 4.15 and Ubuntu picked up 4.15 for its Bionic release, we have Kamal do the
great job of tracking commits to 4.14 and 4.19 and make pull requests so those
can be included in Ubuntu's kernel.

But patches are also submitted to Ubuntu's kernel through other ways and for
other reasons, like when they fix specific bugs tracked at launchpad. It may
happen that such patches match upstream commits that have both landed on
Kamal's tree and directly on Ubuntu's tree.

And by git's distributed nature, the same patch may be applied on different
dates, or it may happen that they are rebased or reapplied, causing them to
have different commit ids, and even different commit dates or commit authors,
or have had their messages changed because of sign-offs.

I didn't investigate the specific case you pointed out, but it may be that with
the explanations above, you may find other differences between those two
commits that might explain what might have happened.

Regards.
Thadeu Cascardo.