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memcg: fix a race when setting memory.swappiness

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(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 <[email protected]>
Acked-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Paul Menage <[email protected]>
Cc: Daisuke Nishimura <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Li Zefan 2009-01-15 13:51:26 -08:00 • committed by Linus Torvalds
commit 068b38c1fa
1 changed files with 9 additions and 1 deletions
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10
mm/memcontrol.c
View file

@ -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;
}