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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>
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0eb253e223
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1 changed files with 9 additions and 1 deletions
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@ -1992,6 +1992,7 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
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{
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{
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struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
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struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
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struct mem_cgroup *parent;
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struct mem_cgroup *parent;
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if (val > 100)
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if (val > 100)
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return -EINVAL;
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return -EINVAL;
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@ -1999,15 +2000,22 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
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return -EINVAL;
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return -EINVAL;
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parent = mem_cgroup_from_cont(cgrp->parent);
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parent = mem_cgroup_from_cont(cgrp->parent);
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cgroup_lock();
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/* If under hierarchy, only empty-root can set this value */
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/* If under hierarchy, only empty-root can set this value */
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if ((parent->use_hierarchy) ||
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if ((parent->use_hierarchy) ||
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(memcg->use_hierarchy && !list_empty(&cgrp->children)))
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(memcg->use_hierarchy && !list_empty(&cgrp->children))) {
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cgroup_unlock();
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return -EINVAL;
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return -EINVAL;
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}
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spin_lock(&memcg->reclaim_param_lock);
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spin_lock(&memcg->reclaim_param_lock);
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memcg->swappiness = val;
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memcg->swappiness = val;
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spin_unlock(&memcg->reclaim_param_lock);
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spin_unlock(&memcg->reclaim_param_lock);
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cgroup_unlock();
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return 0;
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return 0;
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}
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}
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