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

On 3/12/26 21:51, Johannes Weiner wrote:
> 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);

Was about to suggest adding a comment regarding reparenting, but the
comment further below already spells that out now.

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David