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From:   Muchun Song <songmuchun@bytedance.com>
To:     guro@fb.com, hannes@cmpxchg.org, mhocko@kernel.org,
        akpm@linux-foundation.org, shakeelb@google.com,
        vdavydov.dev@gmail.com
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        duanxiongchun@bytedance.com, fam.zheng@bytedance.com,
        bsingharora@gmail.com, shy828301@gmail.com, alexs@kernel.org,
        smuchun@gmail.com, zhengqi.arch@bytedance.com,
        Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH v3 06/12] mm: thp: make split queue lock safe when LRU pages are reparented
Date:   Wed, 16 Feb 2022 19:51:26 +0800
Message-Id: <20220216115132.52602-7-songmuchun@bytedance.com>
In-Reply-To: <20220216115132.52602-1-songmuchun@bytedance.com>
References: <20220216115132.52602-1-songmuchun@bytedance.com>
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Similar to the lruvec lock, we use the same approach to make the split
queue lock safe when LRU pages are reparented.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/huge_memory.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a227731988b3..b8c6e766c91c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -535,9 +535,22 @@ 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(split_queue_memcg(queue) != folio_memcg(folio))) {
+		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;
 }
 
@@ -546,9 +559,19 @@ 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(split_queue_memcg(queue) != folio_memcg(folio))) {
+		spin_unlock_irqrestore(&queue->split_queue_lock, *flags);
+		goto retry;
+	}
+
+	/* See the comments in folio_split_queue_lock(). */
+	rcu_read_unlock();
+
 	return queue;
 }
 
-- 
2.11.0