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Message-ID: <0b4f6c60-fda7-4e5e-8f58-7b8729f966b7@alu.unizg.hr>
Date: Mon, 22 Jan 2024 23:06:40 +0100
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Subject: Re: [BUG][BISECTED] Freeze at loading init ramdisk
To: =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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 "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
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 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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From: Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>
In-Reply-To: <2q2t7mgnpuk2t7wq2tmymxv72oki4uetojkz72xofn7wh45l64@smk3wi6zw54g>
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On 1/22/24 11:20, Uwe Kleine-König wrote:
> On Thu, Jan 18, 2024 at 09:04:05PM +0100, Mirsad Todorovac wrote:
>>
>>
>> On 1/18/24 08:45, Uwe Kleine-König wrote:
>>> Hello Mirsad,
>>>
>>> On Wed, Jan 17, 2024 at 07:47:49PM +0100, Mirsad Todorovac wrote:
>>>> On 1/16/24 01:32, Mirsad Todorovac wrote:
>>>>> On the Ubuntu 22.04 LTS Jammy platform, on a mainline vanilla torvalds tree kernel, the boot
>>>>> freezes upon first two lines and before any systemd messages.
>>>>>
>>>>> (Please find the config attached.)
>>>>>
>>>>> Bisecting the bug led to this result:
>>>>>
>>>>> marvin@defiant:~/linux/kernel/linux_torvalds$ git bisect good
>>>>> d97a78423c33f68ca6543de510a409167baed6f5 is the first bad commit
>>>>> commit d97a78423c33f68ca6543de510a409167baed6f5
>>>>> Merge: 61da593f4458 689237ab37c5
>>>>> Author: Linus Torvalds <torvalds@linux-foundation.org>
>>>>> Date:   Fri Jan 12 14:38:08 2024 -0800
>>>>>
>>>>> [...]
>>>>>
>>>>> Hope this helps.
>>>>
>>>> P.S.
>>>>
>>>> As I see that this is a larger merge commit, with 5K+ lines changed, I don't think I can
>>>> bisect further to determine the culprit.
>>>
>>> Actually it's not that hard. If a merge commit is the first bad commit
>>> for a bisection, either the merge wasn't done correctly (less likely,
>>> looking at d97a78423c33f68ca6543de510a409167baed6f5 I'd bet this isn't
>>> the problem); or changes on different sides conflict or you did
>>> something wrong during bisection.
>>>
>>> To rule out the third option, you can just retest d97a78423c33,
>>> 61da593f4458 and 689237ab37c5. If d97a78423c33 is the only bad one, you
>>> did it right.
>>
>> This was confirmed.
>>
>>> Then to further debug the second option you can find out the offending
>>> commit on each side with a bisection as follows, here for the RHS (i.e.
>>> 689237ab37c5):
>>>
>>> 	git bisect start 689237ab37c5 $(git merge-base 61da593f4458 689237ab37c5)
>>>
>>> and then in each bisection step do:
>>>
>>> 	git merge --no-commit 61da593f4458
>>> 	test if the problem is present
>>> 	git reset --hard
>>> 	git bisect good/bad
>>>
>>> In this case you get merge conflicts in drivers/video/fbdev/amba-clcd.c
>>> and drivers/video/fbdev/vermilion/vermilion.c. In the assumption that
>>> you don't have these enabled in your .config, you can just ignore these.
>>>
>>> Side note: A problem during bisection can be that the .config changes
>>> along the process. You should put your config into (say)
>>> arch/x86/configs/lala_defconfig and do
>>>
>>> 	make lala_defconfig
>>>
>>> before building each step to prevent this.
>>
>> I must have done something wrong:
>>
>> marvin@defiant:~/linux/kernel/linux_torvalds$ git bisect log
>> # bad: [689237ab37c59b9909bc9371d7fece3081683fba] fbdev/intelfb: Remove driver
>> # good: [de927f6c0b07d9e698416c5b287c521b07694cac] Merge tag 's390-6.8-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
>> git bisect start '689237ab37c5' 'de927f6c0b07d9e698416c5b287c521b07694cac'
>> # good: [d9f25b59ed85ae45801cf45fe17eb269b0ef3038] fbdev: Remove support for Carillo Ranch driver
>> git bisect good d9f25b59ed85ae45801cf45fe17eb269b0ef3038
>> # good: [e2e0b838a1849f92612a8305c09aaf31bf824350] video/sticore: Remove info field from STI struct
>> git bisect good e2e0b838a1849f92612a8305c09aaf31bf824350
>> # good: [778e73d2411abc8f3a2d60dbf038acaec218792e] drm/hyperv: Remove firmware framebuffers with aperture helper
>> git bisect good 778e73d2411abc8f3a2d60dbf038acaec218792e
>> # good: [df67699c9cb0ceb70f6cc60630ca938c06773eda] firmware/sysfb: Clear screen_info state after consuming it
>> git bisect good df67699c9cb0ceb70f6cc60630ca938c06773eda
> 
> FTR: Now that you identified df67699c9cb0ce as the culprit, calling
> git bisect good on it was wrong, so something was fishy in your testing
> and it's no surprise the bisection found a wrong result.

Copy that. But it is my first attempt on a bisect of a merge commit, so I will simply
ask to be forgiven. Maybe I forgot "git reset --hard" in some step.

I have to do a thorough homework on the merge commit magic.

Best regards,
Mirsad


> Best regards
> Uwe
>