From: Muchun Song <songmuchun@bytedance.com>

In the near future, a folio will no longer pin its corresponding
memory cgroup. So an lruvec returned by folio_lruvec() could be
released without the rcu read lock or a reference to its memory
cgroup.

In the current patch, the rcu read lock is employed to safeguard
against the release of the lruvec in zswap_folio_swapin().

This serves as a preparatory measure for the reparenting of the
LRU pages.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/zswap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/zswap.c b/mm/zswap.c
index 5d0f8b13a958d..a341814468b95 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -664,8 +664,10 @@ void zswap_folio_swapin(struct folio *folio)
 	struct lruvec *lruvec;
 
 	if (folio) {
+		rcu_read_lock();
 		lruvec = folio_lruvec(folio);
 		atomic_long_inc(&lruvec->zswap_lruvec_state.nr_disk_swapins);
+		rcu_read_unlock();
 	}
 }
 
-- 
2.20.1

On Tue, Oct 28, 2025 at 09:58:31PM +0800, Qi Zheng wrote:
> From: Muchun Song <songmuchun@bytedance.com>
> 
> In the near future, a folio will no longer pin its corresponding
> memory cgroup. So an lruvec returned by folio_lruvec() could be
> released without the rcu read lock or a reference to its memory
> cgroup.
> 
> In the current patch, the rcu read lock is employed to safeguard
> against the release of the lruvec in zswap_folio_swapin().
> 
> This serves as a preparatory measure for the reparenting of the
> LRU pages.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Nhat Pham <nphamcs@gmail.com>
> Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>

-- 
Cheers,
Harry / Hyeonggon