[PATCH v4 19/31] mm: workingset: prevent lruvec release in workingset_refault()

[Qi Zheng]

From: Muchun Song <songmuchun@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Harry Yoo <harry.yoo@xxxxxxxxxx>
Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
---
 mm/workingset.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/workingset.c b/mm/workingset.c
index 79b40f058cd48..5fbf316fb0e71 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -539,6 +539,7 @@ bool workingset_test_recent(void *shadow, bool file, bool *workingset,
 void workingset_refault(struct folio *folio, void *shadow)
 {
 	bool file = folio_is_file_lru(folio);
+	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
 	bool workingset;
 	long nr;
@@ -560,11 +561,12 @@ void workingset_refault(struct folio *folio, void *shadow)
 	 * locked to guarantee folio_memcg() stability throughout.
 	 */
 	nr = folio_nr_pages(folio);
-	lruvec = folio_lruvec(folio);
+	memcg = get_mem_cgroup_from_folio(folio);
+	lruvec = mem_cgroup_lruvec(memcg, folio_pgdat(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 +582,8 @@ void workingset_refault(struct folio *folio, void *shadow)
 		lru_note_cost_refault(folio);
 		mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
 	}
+out:
+	mem_cgroup_put(memcg);
 }
 
 /**
-- 
2.20.1