[v8 PATCH 07/13] mm: vmscan: add shrinker_info_protected() helper

[Yang Shi]

The shrinker_info is dereferenced in a couple of places via 
rcu_dereference_protected
with different calling conventions, for example, using mem_cgroup_nodeinfo 
helper
or dereferencing memcg->nodeinfo[nid]->shrinker_info.  And the later patch
will add more dereference places.

So extract the dereference into a helper to make the code more readable.  No
functional change.

Acked-by: Roman Gushchin <g...@fb.com>
Acked-by: Kirill Tkhai <ktk...@virtuozzo.com>
Acked-by: Vlastimil Babka <vba...@suse.cz>
Signed-off-by: Yang Shi <shy828...@gmail.com>
---
 mm/vmscan.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c94861a3ea3e..fe6e25f46b55 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -192,6 +192,13 @@ static inline int shrinker_map_size(int nr_items)
        return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
 }
 
+static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
+                                                    int nid)
+{
+       return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
+                                        lockdep_is_held(&shrinker_rwsem));
+}
+
 static int expand_one_shrinker_info(struct mem_cgroup *memcg,
                                    int size, int old_size)
 {
@@ -199,8 +206,7 @@ static int expand_one_shrinker_info(struct mem_cgroup 
*memcg,
        int nid;
 
        for_each_node(nid) {
-               old = rcu_dereference_protected(
-                       mem_cgroup_nodeinfo(memcg, nid)->shrinker_info, true);
+               old = shrinker_info_protected(memcg, nid);
                /* Not yet online memcg */
                if (!old)
                        return 0;
@@ -231,7 +237,7 @@ void free_shrinker_info(struct mem_cgroup *memcg)
 
        for_each_node(nid) {
                pn = mem_cgroup_nodeinfo(memcg, nid);
-               info = rcu_dereference_protected(pn->shrinker_info, true);
+               info = shrinker_info_protected(memcg, nid);
                kvfree(info);
                rcu_assign_pointer(pn->shrinker_info, NULL);
        }
@@ -673,8 +679,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int 
nid,
        if (!down_read_trylock(&shrinker_rwsem))
                return 0;
 
-       info = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
-                                        true);
+       info = shrinker_info_protected(memcg, nid);
        if (unlikely(!info))
                goto unlock;
 
-- 
2.26.2