Re: [PATCH v3 3/4] cpuset: settle isolation state when CPUs are given back to parent

[Guopeng Zhang <guopeng.zhang@linux.dev>]

在 2026/11/10 14:24, Ridong Chen 写道:
> 
> 
> On 11/9/2026 11:20 PM, Guopeng Zhang wrote:
>>
>>
>> 在 2026/11/7 20:00, Ridong Chen 写道:
>>> From: Ridong Chen <chenridong@xiaomi.com>
>>>
>>> partition_xcpus_del() only updates isolated_cpus when the partition that
>>> gives back the CPUs has a different state than its parent. CPUs that were
>>> further distributed to descendant isolated partitions are not taken into
>>> account, so isolated_cpus_release() has to be called afterwards in
>>> several places to walk up the ancestors and fix isolated_cpus.
>>>
>>> Make partition_xcpus_del() always set the isolation state of the given
>>> back CPUs to the state of the parent that receives them. As the
>>> effective_xcpus of a partition covers the CPUs distributed to its
>>> descendants, the isolation state of those CPUs is settled at the same
>>> time. Boot-time isolated CPUs are still preserved by isolated_cpu_update().
>>>
>>> compute_partition_effective_cpumask() invalidates a child partition
>>> without going through partition_xcpus_del(), so do the same there: the
>>> CPUs of the invalidated child take the isolation state of its parent.
>>>
>>> As the parent may be shrunk and its effective_xcpus not updated yet,
>>> only do so for the CPUs the parent still owns. This is to keep the
>>> isolation state correct for now, the in-place invalidation here will be
>>> removed later in the partition rework.
>>>
>>> isolated_cpus_update() assumes the old and new states are different,
>>> which no longer holds now that partition_xcpus_del() proceeds regardless
>>> of the states. Drop its @old_prs argument and the WARN_ON_ONCE() so that
>>> it simply sets the isolation state of the given CPUs, and use it
>>> everywhere. The state check in partition_xcpus_add() is dropped as well,
>>> as setting the state is a no-op when the states are the same.
>>>
>>> isolated_cpus_release() is no longer needed and is removed.
>>>
>>
>> Hi Ridong,
>>
>> Would it be worth briefly mentioning in the commit message that this patch also fixes the issue described here?
>>
>> https://lore.kernel.org/all/20261105130344.664336-4-guopeng.zhang@linux.dev/
>>
> Thanks, Guopeng.
> 
> As I replied to Longman, I will add it.
> 

Sorry, I just realized that my comment duplicated Longman's. I had some email connectivity issues and only just received the review emails.

Thanks for the clarification!

Cheers,
Guopeng