[PATCH v1 17/26] mm: workingset: prevent lruvec release in workingset_refault()

Qi Zheng
2025-10-28T14:04:09Z

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_refault().

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 c4d21c15bad51..a69cc7bf9246d 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -560,11 +560,12 @@ void workingset_refault(struct folio *folio, void *shadow)
* locked to guarantee folio_memcg() stability throughout.
*/
nr = folio_nr_pages(folio);
+ rcu_read_lock();
lruvec = folio_lruvec(folio);
mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);

if (!workingset_test_recent(shadow, file, &workingset, true))
- return;
+ goto out;

folio_set_active(folio);
workingset_age_nonresident(lruvec, nr);
@@ -580,6 +581,8 @@ void workingset_refault(struct folio *folio, void *shadow)
lru_note_cost_refault(folio);
mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
}
+out:
+ rcu_read_unlock();
}

/**
--
2.20.1