[PATCH v1 16/26] mm: thp: prevent memory cgroup release in folio_split_queue_lock{_irqsave}()

Qi Zheng
2025-10-28T14:04:01Z

From: Qi Zheng <zhengqi.arch@bytedance.com>

In the near future, a folio will no longer pin its corresponding memory
cgroup. To ensure safety, it will only be appropriate to hold the rcu read
lock or acquire a reference to the memory cgroup returned by
folio_memcg(), thereby preventing it from being released.

In the current patch, the rcu read lock is employed to safeguard against
the release of the memory cgroup in folio_split_queue_lock{_irqsave}().

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
mm/huge_memory.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9d3594df6eedf..067259a9e0809 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1153,13 +1153,25 @@ split_queue_lock_irqsave(int nid, struct mem_cgroup *memcg, unsigned long *flags

static struct deferred_split *folio_split_queue_lock(struct folio *folio)
{
- return split_queue_lock(folio_nid(folio), folio_memcg(folio));
+ struct deferred_split *queue;
+
+ rcu_read_lock();
+ queue = split_queue_lock(folio_nid(folio), folio_memcg(folio));
+ rcu_read_unlock();
+
+ return queue;
}

static struct deferred_split *
folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags)
{
- return split_queue_lock_irqsave(folio_nid(folio), folio_memcg(folio), flags);
+ struct deferred_split *queue;
+
+ rcu_read_lock();
+ queue = split_queue_lock_irqsave(folio_nid(folio), folio_memcg(folio), flags);
+ rcu_read_unlock();
+
+ return queue;
}

static inline void split_queue_unlock(struct deferred_split *queue)
--
2.20.1