[PATCH] mm, memcg: assign shrinker_map before kvfree

Cyrill Gorcunov
2019-09-20T12:29:13Z

Currently there is a small gap between fetching pointer, calling
kvfree and assign its value to nil. In current callgraph it is
not a problem (since memcg_free_shrinker_maps is running from
memcg_alloc_shrinker_maps and mem_cgroup_css_free only) still
this looks suspicious and we can easily eliminate the gap at all.

Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
---
mm/memcontrol.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-tip.git/mm/memcontrol.c
===================================================================
--- linux-tip.git.orig/mm/memcontrol.c
+++ linux-tip.git/mm/memcontrol.c
@@ -364,9 +364,9 @@ static void memcg_free_shrinker_maps(str
for_each_node(nid) {
pn = mem_cgroup_nodeinfo(memcg, nid);
map = rcu_dereference_protected(pn->shrinker_map, true);
+ rcu_assign_pointer(pn->shrinker_map, NULL);
if (map)
kvfree(map);
- rcu_assign_pointer(pn->shrinker_map, NULL);
}
}