Bug 218665 - nohz_full=0 prevents kernel from booting

["Linux regression tracking (Thorsten Leemhuis)" <regressions@leemhuis.info>]

Hi, Thorsten here, the Linux kernel's regression tracker.

I noticed a regression report in bugzilla.kernel.org. As many (most?)
kernel developers don't keep an eye on it, I decided to forward it by mail.

Tejun, apparently it's cause by a change of yours.

Note, you have to use bugzilla to reach the reporter, as I sadly[1] can
not CCed them in mails like this.

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.
> 
> Steps to reproduce:
> - make defconfig
> - set CONFIG_NO_HZ_FULL=y
> - set CONFIG_SUSPEND=n and CONFIG_HIBERNATION=n (to get CONFIG_PM_SLEEP_SMP=n)
> - make
> - qemu-system-x86_64 -nographic -cpu qemu64 -smp cores=2 -m 1024 -kernel arch/x86/boot/bzImage -append "earlyprintk=ttyS0 console=ttyS0 root=/dev/dummy rootwait nohz_full=0"
> 
> I have attached the output of a failed nohz_full=0 boot as
> nohz_full_0.txt and - for reference - the output of a nohz_full=1
> boot as nohz_full_1.txt.
> 
> Interestingly enough, using the deprecated isolcpus parameter to
> enable NO_HZ for cpu0 works. I've attached the output as
> isolcpus_nohz_0.txt.
> 
> Bisecting showed 5797b1c18919cd9c289ded7954383e499f729ce0 as first bad commit.

See the ticket for more details.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
If I did something stupid, please tell me, as explained on that page.

[1] because bugzilla.kernel.org tells users upon registration their
"email address will never be displayed to logged out users"

#regzbot introduced: 5797b1c18919cd9c289ded7954383e499f729ce0
#regzbot from: Friedrich Oslage
#regzbot duplicate https://bugzilla.kernel.org/show_bug.cgi?id=218665
#regzbot title: workqueue: nohz_full=0 prevents booting
#regzbot ignore-activity