Re: [PATCH -mm 5/5] swapcgroup (v3): implement force_empty

[yamamoto-jCdQPDEk3idL9jVzuh4AOg@public.gmane.org (YAMAMOTO Takashi)]

hi,

> +/*
> + * uncharge all the entries that are charged to the group.
> + */
> +void __swap_cgroup_force_empty(struct mem_cgroup *mem)
> +{
> +	struct swap_info_struct *p;
> +	int type;
> +
> +	spin_lock(&swap_lock);
> +	for (type = swap_list.head; type >= 0; type = swap_info[type].next) {
> +		p = swap_info + type;
> +
> +		if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) {
> +			unsigned int i = 0;
> +
> +			spin_unlock(&swap_lock);

what prevents the device from being swapoff'ed while you drop swap_lock?

YAMAMOTO Takashi

> +			while ((i = find_next_to_unuse(p, i, mem)) != 0) {
> +				spin_lock(&swap_lock);
> +				if (p->swap_map[i] && p->memcg[i] == mem)
> +					swap_cgroup_uncharge(p, i);
> +				spin_unlock(&swap_lock);
> +			}
> +			spin_lock(&swap_lock);
> +		}
> +	}
> +	spin_unlock(&swap_lock);
> +
> +	return;
> +}
>  #endif