[RFC PATCH 10/15] mm: thp: make deferred split queue lock safe when the LRU pages reparented

[Muchun Song]

Similar to lruvec lock, we use the same approach to make the lock safe
when the LRU pages reparented.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/huge_memory.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 186dc11e8992..434cc7283a64 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -496,6 +496,8 @@ static struct deferred_split *lock_split_queue(struct page *page)
 	struct deferred_split *queue;
 	struct mem_cgroup *memcg;
 
+	rcu_read_lock();
+retry:
 	memcg = page_memcg(compound_head(page));
 	if (memcg)
 		queue = &memcg->deferred_split_queue;
@@ -503,6 +505,17 @@ static struct deferred_split *lock_split_queue(struct page *page)
 		queue = &NODE_DATA(page_to_nid(page))->deferred_split_queue;
 	spin_lock(&queue->split_queue_lock);
 
+	if (unlikely(memcg != page_memcg(page))) {
+		spin_unlock(&queue->split_queue_lock);
+		goto retry;
+	}
+
+	/*
+	 * Preemption is disabled in the internal of spin_lock, which can serve
+	 * as RCU read-side critical sections.
+	 */
+	rcu_read_unlock();
+
 	return queue;
 }
 
@@ -512,6 +525,8 @@ static struct deferred_split *lock_split_queue_irqsave(struct page *page,
 	struct deferred_split *queue;
 	struct mem_cgroup *memcg;
 
+	rcu_read_lock();
+retry:
 	memcg = page_memcg(compound_head(page));
 	if (memcg)
 		queue = &memcg->deferred_split_queue;
@@ -519,6 +534,17 @@ static struct deferred_split *lock_split_queue_irqsave(struct page *page,
 		queue = &NODE_DATA(page_to_nid(page))->deferred_split_queue;
 	spin_lock_irqsave(&queue->split_queue_lock, *flags);
 
+	if (unlikely(memcg != page_memcg(page))) {
+		spin_unlock_irqrestore(&queue->split_queue_lock, *flags);
+		goto retry;
+	}
+
+	/*
+	 * Preemption is disabled in the internal of spin_lock, which can serve
+	 * as RCU read-side critical sections.
+	 */
+	rcu_read_unlock();
+
 	return queue;
 }
 #else
-- 
2.11.0