memcg: fix a race when setting memory.swappiness

[linux-2.6-omap-h63xx.git] / mm / memcontrol.c

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f0dc076adf05730dc9530d6471cc094a24cf066b..4d0ea3ceba6d2e40431f64f7e8d8c0f3c0022165 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1992,6 +1992,7 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
 {
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
        struct mem_cgroup *parent;
+
        if (val > 100)
                return -EINVAL;
 
@@ -1999,15 +2000,22 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
                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;
 }