mm: swap: prevent lruvec release in lru_gen_clear_refs()

In the near future, a folio will no longer pin its corresponding memory
cgroup.  So an lruvec returned by folio_lruvec() could be released without
the rcu read lock or a reference to its memory cgroup.

In the current patch, the rcu read lock is employed to safeguard against
the release of the lruvec in lru_gen_clear_refs().

This serves as a preparatory measure for the reparenting of the LRU pages.

Link: https://lore.kernel.org/986cd26227191a48a7c34a2a15812d361f4ebd53.1772711148.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/mm/swap.c b/mm/swap.c
index 23df893e2ed71ab7a907a2234188348d33e0b4ef..009b32d6d3444062220dd4b8f93c6169f038d971 100644 (file)
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -412,18 +412,20 @@ static void lru_gen_inc_refs(struct folio *folio)
 
 static bool lru_gen_clear_refs(struct folio *folio)
 {
-       struct lru_gen_folio *lrugen;
        int gen = folio_lru_gen(folio);
        int type = folio_is_file_lru(folio);
+       unsigned long seq;
 
        if (gen < 0)
                return true;
 
        set_mask_bits(&folio->flags.f, LRU_REFS_FLAGS | BIT(PG_workingset), 0);
 
-       lrugen = &folio_lruvec(folio)->lrugen;
+       rcu_read_lock();
+       seq = READ_ONCE(folio_lruvec(folio)->lrugen.min_seq[type]);
+       rcu_read_unlock();
        /* whether can do without shuffling under the LRU lock */
-       return gen == lru_gen_from_seq(READ_ONCE(lrugen->min_seq[type]));
+       return gen == lru_gen_from_seq(seq);
 }
 
 #else /* !CONFIG_LRU_GEN */