linux-kernel - Re: i915 4.5 bugfix backport and release management issue?

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Date:	Tue, 29 Mar 2016 09:16:09 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
Cc:	DRI <dri-devel@...ts.freedesktop.org>,
	Dave Airlie <airlied@...hat.com>,
	Matt Roper <matthew.d.roper@...el.com>,
	Jani Nikula <jani.nikula@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: i915 4.5 bugfix backport and release management issue?

On Tue, Mar 29, 2016 at 12:49 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Tue, Mar 29, 2016 at 12:43 AM, Daniel Vetter <daniel.vetter@...ll.ch> wrote:
>> On Tue, Mar 29, 2016 at 4:39 AM, Andy Lutomirski <luto@...capital.net> wrote:
>>> AFAICT something got rather screwed up in i915 land for 4.5.
>>>
>>> $ git log --oneline --grep='Pretend cursor is always on' v4.5
>>> drivers/gpu/drm/i915/
>>> e2e407dc093f drm/i915: Pretend cursor is always on for ILK-style WM
>>> calculations (v2)
>>>
>>> $ git log --oneline --grep='Pretend cursor is always on' v4.6-rc1
>>> drivers/gpu/drm/i915/
>>> e2e407dc093f drm/i915: Pretend cursor is always on for ILK-style WM
>>> calculations (v2)
>>> b2435692dbb7 drm/i915: Pretend cursor is always on for ILK-style WM
>>> calculations (v2)
>>>
>>> The two patches there are almost, but not quite, the same thing, which
>>> makes me wonder how they both ended up in Linus' tree without an
>>> obvious merge conflict.
>>>
>>> I have no idea what caused this.  However, I think (on very little
>>> inspection, but it's consistent with problems I have with 4.5 on my
>>> laptop) that the first one is an *incorrect* fix for a regression in
>>> 4.5 and the second is a correct fix for the same regression.  4.6-rc1
>>> seems okay.
>>>
>>> I reported the regression and everyone involved has known about it for
>>> weeks.  Nonetheless, 4.5 final is busted.
>>
>> Quoting from e2e407dc093f
>>
>> "(cherry picked from commit b2435692dbb709d4c8ff3b2f2815c9b8423b72bb)"
>>
>> i.e. this is intentionally twice in the history. We started to soak
>> bugfixes in -next and then cherry pick them because we had too much
>> fun with things blowing up, and also too much fun with really messy
>> conflicts. It's not a botched patch in 4.5 or anything else nefarious
>> at all.
>
> Bah, sorry, I read it wrong.  They have the same final state but they
> were on different bases.  I somehow reversed this in my head and
> thought they had the same initial state and different final states.
>

Also, sorry for the excessive diatribe.  I plead sleepiness and
mis-reading of code.

--Andy