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Commit 7941cb02 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: make cgroup_event hold onto cgroup_subsys_state instead of cgroup 



Currently, each registered cgroup_event holds an extra reference to
the cgroup.  This is a bit weird as events are subsystem specific and
will also be incorrect in the planned unified hierarchy as css
(cgroup_subsys_state) may come and go dynamically across the lifetime
of a cgroup.  Holding onto cgroup won't prevent the target css from
going away.

Update cgroup_event to hold onto the css the traget file belongs to
instead of cgroup.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
parent 9fa4db33

kernel/cgroup.c

+12 −14
Original line number Diff line number Diff line
@@ -3969,7 +3969,6 @@ static void cgroup_event_remove(struct work_struct *work) 
	struct cgroup_event *event = container_of(work, struct cgroup_event,

			remove);

	struct cgroup_subsys_state *css = event->css;

	struct cgroup *cgrp = css->cgroup;



	remove_wait_queue(event->wqh, &event->wait);
@@ -3980,7 +3979,7 @@ static void cgroup_event_remove(struct work_struct *work) 


	eventfd_ctx_put(event->eventfd);

	kfree(event);

	cgroup_dput(cgrp);

	css_put(css);

}



/*
@@ -4103,12 +4102,16 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css, 
		goto out_put_cfile;

	}



	/* determine the css of @cfile and associate @event with it */

	/*

	 * Determine the css of @cfile and associate @event with it.

	 * Remaining events are automatically removed on cgroup destruction

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

	 */

	rcu_read_lock();



	ret = -EINVAL;

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

	if (event->css)

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

		ret = 0;



	rcu_read_unlock();
@@ -4122,28 +4125,21 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css, 
	cgrp_cfile = __d_cgrp(cfile->f_dentry->d_parent);

	if (cgrp_cfile != cgrp) {

		ret = -EINVAL;

		goto out_put_cfile;

		goto out_put_css;

	}



	if (!event->cft->register_event || !event->cft->unregister_event) {

		ret = -EINVAL;

		goto out_put_cfile;

		goto out_put_css;

	}



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

			event->eventfd, buffer);

	if (ret)

		goto out_put_cfile;

		goto out_put_css;



	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

	 * directory dentry to do that.

	 */

	dget(cgrp->dentry);



	spin_lock(&cgrp->event_list_lock);

	list_add(&event->list, &cgrp->event_list);

	spin_unlock(&cgrp->event_list_lock);
@@ -4153,6 +4149,8 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css, 


	return 0;



out_put_css:

	css_put(event->css);

out_put_cfile:

	fput(cfile);

out_put_eventfd: