[PATCH v1 20/26] mm: workingset: prevent lruvec release in workingset_activation()

Qi Zheng
2025-10-28T14:04:29Z

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 workingset_activation().

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

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
mm/workingset.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/workingset.c b/mm/workingset.c
index a69cc7bf9246d..d0eb3636dcd1d 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -595,8 +595,11 @@ void workingset_activation(struct folio *folio)
* Filter non-memcg pages here, e.g. unmap can call
* mark_page_accessed() on VDSO pages.
*/
- if (mem_cgroup_disabled() || folio_memcg_charged(folio))
+ if (mem_cgroup_disabled() || folio_memcg_charged(folio)) {
+ rcu_read_lock();
workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
+ rcu_read_unlock();
+ }
}

/*
--
2.20.1