cgroup: restore the call to eventfd->poll()

I mistakenly removed the call to eventfd->poll() while I was actually intending to remove the return value...

Calling evenfd->poll() will hook cgroup_event_wake() to the poll waitqueue, which will be called to unregister eventfd when rmdir a cgroup or close eventfd.

---
 kernel/cgroup.c | 2 ++
 1 file changed, 2 insertions(+)

index a45aa12..4b0f2ef 100644
@@ -3882,6 +3882,8 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
 	if (ret)
 		goto fail;
 
+	efile->f_op->poll(efile, &event->pt);
+
 	/*
 	 * Events should be removed after rmdir of cgroup directory, but before
 	 * destroying subsystem state objects. Let's take reference to cgroup

1.8.0.2

Applied to cgroup/for-3.10. It'd have been better if the patch description pointed to the specific commit which caused the problem.

Thanks.

tejun