Re: [PATCH 13/33] cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset

Waiman Long
2025-11-05T19:40:03Z

On 11/5/25 10:45 AM, Frederic Weisbecker wrote:
>>> + if (!trial)
>>> + return -ENOMEM;
>>> +
>>> + cpumask_andnot(trial, housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT), mask);
>>> + if (!cpumask_intersects(trial, cpu_online_mask)) {
>>> + kfree(trial);
>>> + return -EINVAL;
>>> + }
>>> +
>>> + if (!housekeeping.flags)
>>> + static_branch_enable(&housekeeping_overridden);
>>> +
>>> + if (!(housekeeping.flags & BIT(type)))
>>> + old = housekeeping_cpumask_dereference(type);
>>> + else
>>> + WRITE_ONCE(housekeeping.flags, housekeeping.flags | BIT(type));
>>> + rcu_assign_pointer(housekeeping.cpumasks[type], trial);
>>> +
>>> + synchronize_rcu();
>>> +
>>> + kfree(old);
>> If "isolcpus" boot command line option is set, old can be a pointer to the
>> boot time memblock area which isn't a pointer that can be handled by the
>> slab allocator AFAIU. I don't know the exact consequence, but it may not be
>> good. One possible solution I can think of is to make HK_TYPE_DOMAIN and
>> HK_TYPE_DOMAIN_ROOT point to the same memblock pointer and don't pass the
>> old HK_TYPE_DOMAIN pointer to kfree() if it matches HK_TYPE_DOMAIN_BOOT one.
>> Alternatively, we can just set the HK_TYPE_DOMAIN_BOOT pointer at boot and
>> make HK_TYPE_DOMAIN falls back to HK_TYPE_DOMAIN_BOOT if not set.
> Have a look at housekeeping_init() which reallocates the memblock
> allocated memory with kmalloc to avoid these troubles.

Ah your previous patch of this series did that. I was thinking about the
existing kernel code at the time. So you can ignore that comment.

Thanks,
Longman