Re: [PATCH v1 25/26] mm: memcontrol: eliminate the problem of dying memory cgroup for LRU folios

[Chen Ridong]

On 2025/10/28 21:58, Qi Zheng wrote:
>  static void reparent_locks(struct mem_cgroup *src, struct mem_cgroup *dst)
>  {
> +	int nid, nest = 0;
> +
>  	spin_lock_irq(&objcg_lock);
> +	for_each_node(nid) {
> +		spin_lock_nested(&mem_cgroup_lruvec(src,
> +				 NODE_DATA(nid))->lru_lock, nest++);
> +		spin_lock_nested(&mem_cgroup_lruvec(dst,
> +				 NODE_DATA(nid))->lru_lock, nest++);
> +	}
>  }
>  
>  static void reparent_unlocks(struct mem_cgroup *src, struct mem_cgroup *dst)
>  {
> +	int nid;
> +
> +	for_each_node(nid) {
> +		spin_unlock(&mem_cgroup_lruvec(dst, NODE_DATA(nid))->lru_lock);
> +		spin_unlock(&mem_cgroup_lruvec(src, NODE_DATA(nid))->lru_lock);
> +	}
>  	spin_unlock_irq(&objcg_lock);
>  }
>  

The lock order follows S0→D0→S1→D1→…, and the correct unlock sequence should be Dn→Sn→…→D1→S0

However, the current unlock implementation uses D0→S0→D1→S1→…

I’m not certain whether this unlock order will cause any issues—could this lead to potential
problems like deadlocks or lock state inconsistencies?

-- 
Best regards,
Ridong