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

Waiman Long
2025-10-21T13:39:18Z

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