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>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
---
mm/huge_memory.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 99515838faa51..eb611239c1a74 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1154,13 +1154,29 @@ 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));
+ /*
+ * The memcg destruction path is acquiring the split queue lock for
+ * reparenting. Once you have it locked, it's safe to drop the rcu lock.
+ */
+ 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