[PATCH v2 3/7] mm: list_lru: move list dead check to lock_list_lru_of_memcg()

Johannes Weiner
2026-03-12T20:53:40Z

Only the MEMCG variant of lock_list_lru() needs to check if there is a
race with cgroup deletion and list reparenting. Move the check to the
caller, so that the next patch can unify the lock_list_lru() variants.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
mm/list_lru.c | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index e873bc26a7ef..1a39ff490643 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -68,17 +68,12 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
return &lru->node[nid].lru;
}

-static inline bool lock_list_lru(struct list_lru_one *l, bool irq)
+static inline void lock_list_lru(struct list_lru_one *l, bool irq)
{
if (irq)
spin_lock_irq(&l->lock);
else
spin_lock(&l->lock);
- if (unlikely(READ_ONCE(l->nr_items) == LONG_MIN)) {
- unlock_list_lru(l, irq);
- return false;
- }
- return true;
}

static inline struct list_lru_one *
@@ -90,9 +85,13 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
rcu_read_lock();
again:
l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
- if (likely(l) && lock_list_lru(l, irq)) {
- rcu_read_unlock();
- return l;
+ if (likely(l)) {
+ lock_list_lru(l, irq);
+ if (likely(READ_ONCE(l->nr_items) != LONG_MIN)) {
+ rcu_read_unlock();
+ return l;
+ }
+ unlock_list_lru(l, irq);
}
/*
* Caller may simply bail out if raced with reparenting or
--
2.53.0