linux-kernel - [PATCH] mm, memcg: assign shrinker

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Message-ID: <20190920122907.GG2507@uranus.lan>
Date:   Fri, 20 Sep 2019 15:29:07 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Linux MM <linux-mm@...ck.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>
Subject: [PATCH] mm, memcg: assign shrinker_map before kvfree

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@...xchg.org>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: Kirill Tkhai <ktkhai@...tuozzo.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@...il.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);
 	}
 }