Re: [BUG] cpuset: empty sched domain with isolcpus=domain, panic at CPU offline

[Waiman Long <longman@redhat.com>]

On 11/8/26 1:46 PM, Mathieu Desnoyers wrote:
> On 2026-11-08 13:35, Waiman Long wrote:
> [...]
>> Yes, we are going to add the check to make sure that there will be at
>> least one housekeeping CPU left for the top_cpuset sched domain.
>>
>> See
>> https://lore.kernel.org/lkml/20261105130344.664336-1-guopeng.zhang@linux.dev/
> Thanks, I had missed that series. Refusing such a partition is a better
> fix than giving the top cpuset no sched domain.
>
>> This patch is correct AFAICS. I am not against it but it may not be
>> necessary after we make sure that there is at least one HK online CPU in
>> the top sched domain.
> Then I will drop my patch and rely on Guopeng's series. I can test its
> v3 on the setup that hit the panic: 5 vCPUs with isolcpus=domain,0,1.
>
> By my reading, your _cpu_down() patch covers a case that cpuset cannot
> fix. With no partition, the last online housekeeping CPU could go
> offline. No partition could then give one back.

Yes, that is the point.

Cheers,
Longman