memcg: cgroup_write_event_control() now knows @css is for memcg

 * Input must be in format '<event_fd> <control_fd> <args>'.

 * Interpretation of args is defined by control file implementation.

 */

static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,

static int cgroup_write_event_control(struct cgroup_subsys_state *css,

				      struct cftype *cft, const char *buffer)

{

	struct cgroup *cgrp = dummy_css->cgroup;

	struct cgroup *cgrp = css->cgroup;

	struct cgroup_event *event;

	struct cgroup_subsys_state *cfile_css;

	unsigned int efd, cfd;

	if (!event)

		return -ENOMEM;

	event->css = css;

	INIT_LIST_HEAD(&event->list);

	init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);

	init_waitqueue_func_entry(&event->wait, cgroup_event_wake);

		goto out_put_cfile;

	}

	if (!event->cft->ss) {

		ret = -EBADF;

		goto out_put_cfile;

	}

	/*

	 * Determine the css of @cfile, verify it belongs to the same

	 * cgroup as cgroup.event_control, and associate @event with it.

	 * Remaining events are automatically removed on cgroup destruction

	 * but the removal is asynchronous, so take an extra ref.

	 * Verify @cfile should belong to @css.  Also, remaining events are

	 * automatically removed on cgroup destruction but the removal is

	 * asynchronous, so take an extra ref on @css.

	 */

	rcu_read_lock();

	ret = -EINVAL;

	event->css = cgroup_css(cgrp, event->cft->ss);

	cfile_css = css_from_dir(cfile.file->f_dentry->d_parent, event->cft->ss);

	if (event->css && event->css == cfile_css && css_tryget(event->css))

	cfile_css = css_from_dir(cfile.file->f_dentry->d_parent,

				 &mem_cgroup_subsys);

	if (cfile_css == css && css_tryget(css))

		ret = 0;

	rcu_read_unlock();

		goto out_put_css;

	}

	ret = event->cft->register_event(event->css, event->cft,

	ret = event->cft->register_event(css, event->cft,

			event->eventfd, buffer);

	if (ret)

		goto out_put_css;

	return 0;

out_put_css:

	css_put(event->css);

	css_put(css);

out_put_cfile:

	fdput(cfile);

out_put_eventfd: