[0/1] On DRM -> stable process

Message

Fedor Pchelkin Oct. 29, 2024, 1:31 p.m. UTC

Hi all,

I'm writing as a bystander working with 6.1.y stable branch and possibly
lacking some context with the established DRM -> stable patch flow, Cc'ing
a large number of people.

The commit being reverted from 6.1.y is the one that duplicates the
changes already backported to that branch with another commit. It is
essentially a "similar" commit but cherry-picked at some point during the
DRM development process.

The duplicate has no runtime effect but should not actually remain in the
stable trees. It was already reverted [1] from 6.6/6.10/6.11 but still made
its way later to 6.1.

[1]: https://lore.kernel.org/stable/[e-mail]/T/#u

At [1] Greg KH also stated that the observed problems are quite common
while backporting DRM patches to stable trees. The current duplicate patch
has in every sense a cosmetic impact but in other circumstances and for
other patches this may have gone wrong.

So, is there any way to adjust this process?

BTW, a question to the stable-team: what Git magic (3-way-merge?) let the
duplicate patch be applied successfully? The patch context in stable trees
was different to that moment so should the duplicate have been expected to
fail to be applied?

--
Fedor

Comments

Sasha Levin Oct. 29, 2024, 2:20 p.m. UTC | #1

On Tue, Oct 29, 2024 at 04:31:40PM +0300, Fedor Pchelkin wrote:
>BTW, a question to the stable-team: what Git magic (3-way-merge?) let the
>duplicate patch be applied successfully? The patch context in stable trees
>was different to that moment so should the duplicate have been expected to
>fail to be applied?

Just plain git... Try it yourself :)

$ git checkout 282f0a482ee6
HEAD is now at 282f0a482ee61 drm/amd/display: Skip Recompute DSC Params if no Stream on Link

$ git cherry-pick 7c887efda1
Auto-merging drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
[detached HEAD 2a1c937960abd] drm/amd/display: Skip Recompute DSC Params if no Stream on Link
  Author: Fangzhi Zuo <[e-mail]>
  Date: Fri Jul 12 16:30:03 2024 -0400
  1 file changed, 3 insertions(+)

$ git log -2 --oneline
2a1c937960abd (HEAD) drm/amd/display: Skip Recompute DSC Params if no Stream on Link
282f0a482ee61 drm/amd/display: Skip Recompute DSC Params if no Stream on Link

Fedor Pchelkin Oct. 29, 2024, 3:12 p.m. UTC | #2

On Tue, 29. Oct 10:20, Sasha Levin wrote:
> On Tue, Oct 29, 2024 at 04:31:40PM +0300, Fedor Pchelkin wrote:
> > BTW, a question to the stable-team: what Git magic (3-way-merge?) let the
> > duplicate patch be applied successfully? The patch context in stable trees
> > was different to that moment so should the duplicate have been expected to
> > fail to be applied?
> 
> Just plain git... Try it yourself :)
> 
> $ git checkout 282f0a482ee6
> HEAD is now at 282f0a482ee61 drm/amd/display: Skip Recompute DSC Params if no Stream on Link
> 
> $ git cherry-pick 7c887efda1

7c887efda1 is the commit backported to linux-6.1.y. Of course it will apply
there.

What I mean is that the upstream commit for 7c887efda1 is 8151a6c13111b465dbabe07c19f572f7cbd16fef.

And cherry-picking 8151a6c13111b465dbabe07c19f572f7cbd16fef to linux-6.1.y
on top of 282f0a482ee6 will not result in duplicating the change, at least
with my git configuration.

I just don't understand how a duplicating if-statement could be produced in
result of those cherry-pick'ings and how the content of 7c887efda1 was
generated.

$ git checkout 282f0a482ee6
HEAD is now at 282f0a482ee6 drm/amd/display: Skip Recompute DSC Params if no Stream on Link

$ git cherry-pick 8151a6c13111b465dbabe07c19f572f7cbd16fef
Auto-merging drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
HEAD detached at 282f0a482ee6
You are currently cherry-picking commit 8151a6c13111.
  (all conflicts fixed: run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)
The previous cherry-pick is now empty, possibly due to conflict resolution.
If you wish to commit it anyway, use:

    git commit --allow-empty

Otherwise, please use 'git cherry-pick --skip'

> Auto-merging drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> [detached HEAD 2a1c937960abd] drm/amd/display: Skip Recompute DSC Params if no Stream on Link
>  Author: Fangzhi Zuo <[e-mail]>
>  Date: Fri Jul 12 16:30:03 2024 -0400
>  1 file changed, 3 insertions(+)
> 
> $ git log -2 --oneline
> 2a1c937960abd (HEAD) drm/amd/display: Skip Recompute DSC Params if no Stream on Link
> 282f0a482ee61 drm/amd/display: Skip Recompute DSC Params if no Stream on Link
> 
> -- 
> Thanks,
> Sasha