From 068b38c1fa7a9210608f27ac521897ccc5f9b726 Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Thu, 15 Jan 2009 13:51:26 -0800 Subject: [PATCH] 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 Acked-by: KAMEZAWA Hiroyuki Cc: Balbir Singh Cc: Paul Menage Cc: Daisuke Nishimura Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index f0dc076adf05..4d0ea3ceba6d 100644 --- 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; } -- 2.39.2