[PATCH RFC 25/28] mm: thp: prepare for reparenting LRU pages for split queue lock

[Muchun Song]

Analogous to the mechanism employed for the lruvec lock, we adopt
an identical strategy to ensure the safety of the split queue lock
during the reparenting process of LRU folios.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/huge_memory.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d2bc943a40e8..813334994f84 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1100,8 +1100,14 @@ static struct deferred_split *folio_split_queue_lock(struct folio *folio)
 {
 	struct deferred_split *queue;
 
+	rcu_read_lock();
+retry:
 	queue = folio_split_queue(folio);
 	spin_lock(&queue->split_queue_lock);
+	if (unlikely(folio_split_queue_memcg(folio, queue) != folio_memcg(folio))) {
+		spin_unlock(&queue->split_queue_lock);
+		goto retry;
+	}
 
 	return queue;
 }
@@ -1111,8 +1117,14 @@ folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags)
 {
 	struct deferred_split *queue;
 
+	rcu_read_lock();
+retry:
 	queue = folio_split_queue(folio);
 	spin_lock_irqsave(&queue->split_queue_lock, *flags);
+	if (unlikely(folio_split_queue_memcg(folio, queue) != folio_memcg(folio))) {
+		spin_unlock_irqrestore(&queue->split_queue_lock, *flags);
+		goto retry;
+	}
 
 	return queue;
 }
@@ -1120,12 +1132,14 @@ folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags)
 static inline void split_queue_unlock(struct deferred_split *queue)
 {
 	spin_unlock(&queue->split_queue_lock);
+	rcu_read_unlock();
 }
 
 static inline void split_queue_unlock_irqrestore(struct deferred_split *queue,
 						 unsigned long flags)
 {
 	spin_unlock_irqrestore(&queue->split_queue_lock, flags);
+	rcu_read_unlock();
 }
 
 static inline bool is_transparent_hugepage(const struct folio *folio)
-- 
2.20.1