buffer: prevent memory cgroup release in folio_alloc_buffers()

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 function get_mem_cgroup_from_folio() is employed
to safeguard against the release of the memory cgroup.  This serves as a
preparatory measure for the reparenting of the LRU pages.

Link: https://lore.kernel.org/d6d48fdcf329c549373ac0a1c80fd9f38067e34e.1772711148.git.zhengqi.arch@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
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>
Cc: Allen Pais <apais@linux.microsoft.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chen Ridong <chenridong@huawei.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Imran Khan <imran.f.khan@oracle.com>
Cc: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yosry Ahmed <yosry@kernel.org>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/buffer.c b/fs/buffer.c
index f3122160ee2d606ff7d20d1c6b1e6df6adbc2b48..bbe42edad59dc45ee94229b494499652de8abfac 100644 (file)
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -922,8 +922,7 @@ struct buffer_head *folio_alloc_buffers(struct folio *folio, unsigned long size,
        long offset;
        struct mem_cgroup *memcg, *old_memcg;
 
-       /* The folio lock pins the memcg */
-       memcg = folio_memcg(folio);
+       memcg = get_mem_cgroup_from_folio(folio);
        old_memcg = set_active_memcg(memcg);
 
        head = NULL;
@@ -944,6 +943,7 @@ struct buffer_head *folio_alloc_buffers(struct folio *folio, unsigned long size,
        }
 out:
        set_active_memcg(old_memcg);
+       mem_cgroup_put(memcg);
        return head;
 /*
  * In case anything failed, we just free everything we got.