memcg: fix a race when setting memory.swappiness
(suppose: memcg->use_hierarchy == 0 and memcg->swappiness == 60)
echo 10 > /memcg/0/swappiness |
mem_cgroup_swappiness_write() |
... | echo 1 > /memcg/0/use_hierarchy
| mkdir /mnt/0/1
| sub_memcg->swappiness = 60;
memcg->swappiness = 10; |
In the above scenario, we end up having 2 different swappiness
values in a single hierarchy.
We should hold cgroup_lock() when cheking cgrp->children list.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f0dc076..4d0ea3c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1992,6 +1992,7 @@
{
struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
struct mem_cgroup *parent;
+
if (val > 100)
return -EINVAL;
@@ -1999,15 +2000,22 @@
return -EINVAL;
parent = mem_cgroup_from_cont(cgrp->parent);
+
+ cgroup_lock();
+
/* If under hierarchy, only empty-root can set this value */
if ((parent->use_hierarchy) ||
- (memcg->use_hierarchy && !list_empty(&cgrp->children)))
+ (memcg->use_hierarchy && !list_empty(&cgrp->children))) {
+ cgroup_unlock();
return -EINVAL;
+ }
spin_lock(&memcg->reclaim_param_lock);
memcg->swappiness = val;
spin_unlock(&memcg->reclaim_param_lock);
+ cgroup_unlock();
+
return 0;
}