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Date:   Wed, 12 Oct 2022 22:20:01 -0700
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To:     Nicholas Piggin <npiggin@gmail.com>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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From:   Guenter Roeck <linux@roeck-us.net>
Subject: Re: [GIT PULL] Please pull powerpc/linux.git powerpc-6.1-1 tag
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On 10/12/22 22:03, Nicholas Piggin wrote:
> On Thu Oct 13, 2022 at 10:21 AM AEST, Guenter Roeck wrote:
>> On Thu, Oct 13, 2022 at 11:03:34AM +1100, Michael Ellerman wrote:
>>> Guenter Roeck <linux@roeck-us.net> writes:
>>>> On Wed, Oct 12, 2022 at 11:20:38AM -0600, Jason A. Donenfeld wrote:
>>>>>
>>>>> I've also managed to not hit this bug a few times. When it triggers,
>>>>> after "kprobes: kprobe jump-optimization is enabled. All kprobes are
>>>>> optimized if possible.", there's a long hang - tens seconds before it
>>>>> continues. When it doesn't trigger, there's no hang at that point in the
>>>>> boot process.
>>>>>
>>>>
>>>> I managed to bisect the problem. See below for results. Reverting the
>>>> offending patch fixes the problem for me.
>>>
>>> Thanks.
>>>
>>> This is probably down to me/us not testing with PREEMPT enabled enough.
>>>
>> Not sure. My configuration has
>>
>> CONFIG_PREEMPT_NONE=y
>> # CONFIG_PREEMPT_VOLUNTARY is not set
>> # CONFIG_PREEMPT is not set
> 
> Thanks very much for helping with this. The config snippet you posted here
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2022-October/249758.html
> has CONFIG_PREEMPT=y. How do you turn that into a .config, olddefconfig?
> 
> I can't reproduce this so far using your config and qemu command line,
> but the patch you've bisected it to definitely could cause this. I'll
> keep trying...
> 

Uuh, sorry, I think I got confused with running multiple bisects on the
same branch, and took the above from a different bisect run. You are
correct, PREEMPT is enabled in the configuration.

Timing is definitely involved; I see the problem more often on a loaded
system. To bisect it, I had to repeat the test for each bisect step
several times (I set the limit to 20 retries; that gave me reliable
results).

Guenter