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cgroup: fix offlining child waiting in cgroup_subtree_control_write()

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cgroup_subtree_control_write() waits for offline to complete
child-by-child before enabling a controller; however, it has a couple
bugs.

* It doesn't initialize the wait_queue_t.  This can lead to infinite
  hang on the following schedule() among other things.

* It forgets to pin the child before releasing cgroup_tree_mutex and
  performing schedule().  The child may already be gone by the time it
  wakes up and invokes finish_wait().  Pin the child being waited on.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2014-05-13 12:10:59 -04:00
parent f21a4f7594
commit 0cee8b7786
1 changed files with 3 additions and 1 deletions
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4
kernel/cgroup.c
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@ -2594,16 +2594,18 @@ retry:
* cases, wait till it's gone using offline_waitq.
*/
cgroup_for_each_live_child(child, cgrp) {
wait_queue_t wait;
DEFINE_WAIT(wait);
if (!cgroup_css(child, ss))
continue;
cgroup_get(child);
prepare_to_wait(&child->offline_waitq, &wait,
TASK_UNINTERRUPTIBLE);
mutex_unlock(&cgroup_tree_mutex);
schedule();
finish_wait(&child->offline_waitq, &wait);
cgroup_put(child);
goto retry;
}