[PATCH v3 3/7] mm: list_lru: move list dead check to lock_list_lru_of_memcg()

[Johannes Weiner]

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.

Reviewed-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 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