linux-kernel - Re: Bug 218665 - nohz_full=0 prevents kernel from booting

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Date: Wed, 17 Apr 2024 07:48:33 +0200
From: "Linux regression tracking (Thorsten Leemhuis)"
 <regressions@...mhuis.info>
To: Tejun Heo <tj@...nel.org>, Bjorn Andersson <andersson@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Linux regressions mailing list <regressions@...ts.linux.dev>
Subject: Re: Bug 218665 - nohz_full=0 prevents kernel from booting

On 17.04.24 01:21, Tejun Heo wrote:
> On Tue, Apr 16, 2024 at 08:08:07AM +0200, Linux regression tracking (Thorsten Leemhuis) wrote:
>> On 12.04.24 04:57, Bjorn Andersson wrote:
>>> On Wed, Apr 10, 2024 at 11:18:04AM +0200, Linux regression tracking (Thorsten Leemhuis) wrote:
>>>> On 08.04.24 00:52, Bjorn Andersson wrote:
>>>>> On Tue, Apr 02, 2024 at 10:17:16AM +0200, Linux regression tracking (Thorsten Leemhuis) wrote:
>>>>>>
>>>>>> Tejun, apparently it's cause by a change of yours.
>>>>>> Quoting from https://bugzilla.kernel.org/show_bug.cgi?id=218665 :
>>>>>>
>>>>>>> booting the current kernel (6.9.0-rc1, master/712e1425) on x86_64
>>>>>>> with nohz_full=0 cause a page fault and prevents the kernel from
>>>>>>> booting.
>>>>> [...]
>>
>> Tejun, I got a bit lost here. Can you help me out please?
>>
>> I'm currently assuming that these two reports have the same cause:
>> https://lore.kernel.org/all/20240402105847.GA24832@redhat.com/T/#u
>> https://bugzilla.kernel.org/show_bug.cgi?id=218665
>>
>> And that both will be fixed by this patch from Oleg Nesterov:
>> https://lore.kernel.org/lkml/20240411143905.GA19288@redhat.com/
>>
>> But well, to me it looks like below issue from Bjorn is different, even
>> if it is caused by the same change -- nevertheless it looks like nobody
>> has looked into this since it was reported about two weeks ago. Or was
>> progress made and I just missed it?
> 
> Can you elaborate why Bjorn's case is different?

Well "not booting at all when using 'nohz_full=0'"[as reported two
times] and "I start neovim, send SIGSTOP (i.e. ^Z) to it, start another
neovim instance and upon sending SIGSTOP to that instance all of
userspace locks up - 100% reproducible."[while no 'nohz_full=0' in use]
at least on the first sight to and outsider sound a lot like different
problems to me -- but of course that impression might be wrong and you
know better about these things.

> I was assuming it was the
> same problem and that Oleg's fixes would address the issue.

Bjorn, could you give it a try?

Ciao, Thorsten