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 <t...@kernel.org>
---
kernel/cgroup.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 07815ef..54fd12d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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;
}
--
1.9.0
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