Re: [PATCH] MIPS: smp: report dying CPU to RCU in stop_this_cpu()

[Jonas Jelonek <jelonek.jonas@gmail.com>]

Hi Sebastian,

I'm not an expert in this area so please correct me if some claim or
explanation is wrong.

On 05.06.26 08:42, Sebastian Andrzej Siewior wrote:
> On 2026-06-04 18:24:07 [+0000], Jonas Jelonek wrote:
> …
>> This issue popped up during kernel bump downstream in OpenWrt from
>> 6.18.33 to 6.18.34, since the suspected change has been backported to
>> 6.18 stable branch [1].
> I would avoid the link and simply write after the backport of the patch
> or so.

Fine with that, I can adjust that in a v2.

>> Call rcutree_report_cpu_dead() once interrupts are disabled, mirroring the
>> generic CPU-hotplug offline path (and arm64's stop handling), so RCU stops
>> waiting on the parked CPUs and grace periods can still complete.
> This is part of cpuhp_report_idle_dead(). Is it now invoked twice? Or is
> something else missing/ different? 

Those seem to be two different paths. To be honest I'm not confident
under which circumstances which of those paths is used to take down
a CPU. In my case, issuing a reboot command reaches smp_send_stop()
where the issue explained in the patch message then happens.

> Sebastian

Best,
Jonas