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

Chen Ridong
2025-11-20T11:56:21Z

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