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.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index bd4de465d5a9..3f14a1310d23 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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