Commit 068b38c1 authored Jan 15, 2009 by Li Zefan Committed by Linus Torvalds Jan 15, 2009

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>

parent 0eb253e2

mm/memcontrol.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}