mm: vmscan: hold write lock to reparent shrinker nr_deferred

For now, reparent_shrinker_deferred() is the only holder of read lock of
shrinker_rwsem.  And it already holds the global cgroup_mutex, so it will
not be called in parallel.

Therefore, in order to convert shrinker_rwsem to shrinker_mutex later,
here we change to hold the write lock of shrinker_rwsem to reparent.

Link: https://lkml.kernel.org/r/20230313112819.38938-7-zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill Tkhai <tkhai@ya.ru>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Christian König <christian.koenig@amd.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Sultan Alsawaf <sultan@kerneltoast.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5c2a224..8c1ae7e 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -445,7 +445,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
                parent = root_mem_cgroup;
 
        /* Prevent from concurrent shrinker_info expand */
-       down_read(&shrinker_rwsem);
+       down_write(&shrinker_rwsem);
        for_each_node(nid) {
                child_info = shrinker_info_protected(memcg, nid);
                parent_info = shrinker_info_protected(parent, nid);
@@ -454,7 +454,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
                        atomic_long_add(nr, &parent_info->nr_deferred[i]);
                }
        }
-       up_read(&shrinker_rwsem);
+       up_write(&shrinker_rwsem);
 }
 
 static bool cgroup_reclaim(struct scan_control *sc)