[PATCH] mm, list_lru: refactor the locking code

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

Cocci is confused by the try lock then release RCU and return logic
here. So separate the try lock part out into a standalone helper. The
code is easier to follow too.

No feature change, fixes:

cocci warnings: (new ones prefixed by >>)
>> mm/list_lru.c:82:3-9: preceding lock on line 77
>> mm/list_lru.c:82:3-9: preceding lock on line 77
   mm/list_lru.c:82:3-9: preceding lock on line 75
   mm/list_lru.c:82:3-9: preceding lock on line 75

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Julia Lawall <julia.lawall@inria.fr>
Closes: https://lore.kernel.org/r/202505252043.pbT1tBHJ-lkp@intel.com/
Signed-off-by: Kairui Song <kasong@tencent.com>
---
 mm/list_lru.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 490473af3122..ec48b5dadf51 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -60,30 +60,34 @@ 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)
+{
+	if (irq)
+		spin_lock_irq(&l->lock);
+	else
+		spin_lock(&l->lock);
+	if (unlikely(READ_ONCE(l->nr_items) == LONG_MIN)) {
+		if (irq)
+			spin_unlock_irq(&l->lock);
+		else
+			spin_unlock(&l->lock);
+		return false;
+	}
+	return true;
+}
+
 static inline struct list_lru_one *
 lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 		       bool irq, bool skip_empty)
 {
 	struct list_lru_one *l;
-	long nr_items;
 
 	rcu_read_lock();
 again:
 	l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
-	if (likely(l)) {
-		if (irq)
-			spin_lock_irq(&l->lock);
-		else
-			spin_lock(&l->lock);
-		nr_items = READ_ONCE(l->nr_items);
-		if (likely(nr_items != LONG_MIN)) {
-			rcu_read_unlock();
-			return l;
-		}
-		if (irq)
-			spin_unlock_irq(&l->lock);
-		else
-			spin_unlock(&l->lock);
+	if (likely(l) && lock_list_lru(l, irq)) {
+		rcu_read_unlock();
+		return l;
 	}
 	/*
 	 * Caller may simply bail out if raced with reparenting or
-- 
2.49.0