[v10 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 <guro@xxxxxx>
Acked-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
---
 mm/vmscan.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7fdfdacf9a1f..ef9f1531a6ee 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)
 {
@@ -201,7 +208,7 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
 
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
-		old = rcu_dereference_protected(pn->shrinker_info, true);
+		old = shrinker_info_protected(memcg, nid);
 		/* Not yet online memcg */
 		if (!old)
 			return 0;
@@ -232,7 +239,7 @@ void free_shrinker_info(struct mem_cgroup *memcg)
 
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
-		info = rcu_dereference_protected(pn->shrinker_info, true);
+		info = shrinker_info_protected(memcg, nid);
 		kvfree(info);
 		rcu_assign_pointer(pn->shrinker_info, NULL);
 	}
@@ -675,8 +682,7 @@ 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