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

[Waiman Long <llong@redhat.com>]

On 10/13/25 4:31 PM, Frederic Weisbecker wrote:
> @@ -80,12 +110,45 @@ EXPORT_SYMBOL_GPL(housekeeping_affine);
>   
>   bool housekeeping_test_cpu(int cpu, enum hk_type type)
>   {
> -	if (housekeeping.flags & BIT(type))
> +	if (READ_ONCE(housekeeping.flags) & BIT(type))
>   		return cpumask_test_cpu(cpu, housekeeping_cpumask(type));
>   	return true;
>   }
>   EXPORT_SYMBOL_GPL(housekeeping_test_cpu);
>   
> +int housekeeping_update(struct cpumask *mask, enum hk_type type)
> +{
> +	struct cpumask *trial, *old = NULL;
> +
> +	if (type != HK_TYPE_DOMAIN)
> +		return -ENOTSUPP;
> +
> +	trial = kmalloc(sizeof(*trial), GFP_KERNEL);
Should you use cpumask_size() instead of sizeof(*trial) as the latter 
can be much bigger?
> +	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.

Cheers,
Longman