Re: [PATCH v4 1/5] hugetlb: add demote hugetlb page sysfs interfaces

[Oscar Salvador <osalvador@suse.de>]

On Thu, Oct 07, 2021 at 11:19:14AM -0700, Mike Kravetz wrote:
> +static ssize_t demote_store(struct kobject *kobj,
> +	       struct kobj_attribute *attr, const char *buf, size_t len)
> +{
> +	unsigned long nr_demote;
> +	unsigned long nr_available;
> +	nodemask_t nodes_allowed, *n_mask;
> +	struct hstate *h;
> +	int err = 0;
> +	int nid;
> +
> +	err = kstrtoul(buf, 10, &nr_demote);
> +	if (err)
> +		return err;
> +	h = kobj_to_hstate(kobj, &nid);
> +
> +	/* Synchronize with other sysfs operations modifying huge pages */
> +	mutex_lock(&h->resize_lock);
> +
> +	if (nid != NUMA_NO_NODE) {
> +		init_nodemask_of_node(&nodes_allowed, nid);
> +		n_mask = &nodes_allowed;
> +	} else {
> +		n_mask = &node_states[N_MEMORY];
> +	}

Why this needs to be protected by the resize_lock? I do not understand
what are we really protecting here and from what.

Besides that, I did not spot anything wrong.

-- 
Oscar Salvador
SUSE Labs