[PATCH v4 47/48] mm: shrinker: hold write lock to reparent shrinker nr_deferred

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

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.

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
 mm/shrinker.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/shrinker.c b/mm/shrinker.c
index fee6f62904fb..a12dede5d21f 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -299,7 +299,7 @@ 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);
@@ -312,7 +312,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
                        }
                }
        }
-       up_read(&shrinker_rwsem);
+       up_write(&shrinker_rwsem);
 }
 #else
 static int shrinker_memcg_alloc(struct shrinker *shrinker)
-- 
2.30.2