Commit 068b38c1 authored by Li Zefan's avatar Li Zefan Committed by Linus Torvalds
Browse files

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: default avatarLi Zefan <lizf@cn.fujitsu.com>
Acked-by: default avatarKAMEZAWA 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0eb253e2
......@@ -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;
}
......
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