Commit f20104de authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: replace cgroup->css_kill_cnt with ->nr_css 



Currently, css (cgroup_subsys_state) lifetime is tied to that of the
associated cgroup.  With the planned unified hierarchy, css's will be
dynamically created and destroyed within the lifetime of a cgroup.  To
enable such usages, css's will be individually RCU protected instead
of being tied to the cgroup.

cgroup->css_kill_cnt is used during cgroup destruction to wait for css
reference count disable; however, this model doesn't work once css's
lifetimes are managed separately from cgroup's.  This patch replaces
it with cgroup->nr_css which is an cgroup_mutex protected integer
counting the number of attached css's.  The count is incremented from
online_css() and decremented after refcnt kill is confirmed.  If the
count reaches zero and the cgroup is marked dead, the second stage of
cgroup destruction is kicked off.  If a cgroup doesn't have any css
attached at the time of rmdir, cgroup_destroy_locked() now invokes the
second stage directly as no css kill confirmation would happen.

cgroup_offline_fn() - the second step of cgroup destruction - is
renamed to cgroup_destroy_css_killed() and now expects to be called
with cgroup_mutex held.

While this patch changes how css destruction is punted to work items,
it shouldn't change any visible behavior.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 223dbc38

include/linux/cgroup.h

+3 −1
Original line number Diff line number Diff line
@@ -171,6 +171,9 @@ struct cgroup { 
	 */

	int id;



	/* the number of attached css's */

	int nr_css;



	/*

	 * We link our 'sibling' struct into our parent's 'children'.

	 * Our children link their 'sibling' into our 'children'.
@@ -234,7 +237,6 @@ struct cgroup { 
	/* For css percpu_ref killing and RCU-protected deletion */

	struct rcu_head rcu_head;

	struct work_struct destroy_work;

	atomic_t css_kill_cnt;



	/* List of events which userspace want to receive */

	struct list_head event_list;

kernel/cgroup.c

+28 −24
Original line number Diff line number Diff line
@@ -218,7 +218,7 @@ static int need_forkexit_callback __read_mostly; 


static struct cftype cgroup_base_files[];



static void cgroup_offline_fn(struct work_struct *work);

static void cgroup_destroy_css_killed(struct cgroup *cgrp);

static int cgroup_destroy_locked(struct cgroup *cgrp);

static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],

			      bool is_add);
@@ -4335,6 +4335,7 @@ static int online_css(struct cgroup_subsys_state *css) 
		ret = ss->css_online(css);

	if (!ret) {

		css->flags |= CSS_ONLINE;

		css->cgroup->nr_css++;

		rcu_assign_pointer(css->cgroup->subsys[ss->subsys_id], css);

	}

	return ret;
@@ -4545,16 +4546,6 @@ static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode) 
	return cgroup_create(c_parent, dentry, mode | S_IFDIR);

}



static void cgroup_css_killed(struct cgroup *cgrp)

{

	if (!atomic_dec_and_test(&cgrp->css_kill_cnt))

		return;



	/* percpu ref's of all css's are killed, kick off the next step */

	INIT_WORK(&cgrp->destroy_work, cgroup_offline_fn);

	schedule_work(&cgrp->destroy_work);

}



/*

 * This is called when the refcnt of a css is confirmed to be killed.

 * css_tryget() is now guaranteed to fail.
@@ -4565,7 +4556,17 @@ static void css_killed_work_fn(struct work_struct *work) 
		container_of(work, struct cgroup_subsys_state, destroy_work);

	struct cgroup *cgrp = css->cgroup;



	cgroup_css_killed(cgrp);

	mutex_lock(&cgroup_mutex);



	/*

	 * If @cgrp is marked dead, it's waiting for refs of all css's to

	 * be disabled before proceeding to the second phase of cgroup

	 * destruction.  If we are the last one, kick it off.

	 */

	if (!--cgrp->nr_css && cgroup_is_dead(cgrp))

		cgroup_destroy_css_killed(cgrp);



	mutex_unlock(&cgroup_mutex);

}



/* css kill confirmation processing requires process context, bounce */
@@ -4634,11 +4635,10 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	 * Use percpu_ref_kill_and_confirm() to get notifications as each

	 * css is confirmed to be seen as killed on all CPUs.  The

	 * notification callback keeps track of the number of css's to be

	 * killed and schedules cgroup_offline_fn() to perform the rest of

	 * destruction once the percpu refs of all css's are confirmed to

	 * be killed.

	 * killed and invokes cgroup_destroy_css_killed() to perform the

	 * rest of destruction once the percpu refs of all css's are

	 * confirmed to be killed.

	 */

	atomic_set(&cgrp->css_kill_cnt, 1);

	for_each_root_subsys(cgrp->root, ss) {

		struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);
@@ -4648,10 +4648,8 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
		 */

		percpu_ref_get(&css->refcnt);



		atomic_inc(&cgrp->css_kill_cnt);

		percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);

	}

	cgroup_css_killed(cgrp);



	/*

	 * Mark @cgrp dead.  This prevents further task migration and child
@@ -4668,6 +4666,15 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
		list_del_init(&cgrp->release_list);

	raw_spin_unlock(&release_list_lock);



	/*

	 * If @cgrp has css's attached, the second stage of cgroup

	 * destruction is kicked off from css_killed_work_fn() after the

	 * refs of all attached css's are killed.  If @cgrp doesn't have

	 * any css, we kick it off here.

	 */

	if (!cgrp->nr_css)

		cgroup_destroy_css_killed(cgrp);



	/*

	 * Clear and remove @cgrp directory.  The removal puts the base ref

	 * but we aren't quite done with @cgrp yet, so hold onto it.
@@ -4693,7 +4700,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
};



/**

 * cgroup_offline_fn - the second step of cgroup destruction

 * cgroup_destroy_css_killed - the second step of cgroup destruction

 * @work: cgroup->destroy_free_work

 *

 * This function is invoked from a work item for a cgroup which is being
@@ -4702,14 +4709,13 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
 * is the second step of destruction described in the comment above

 * cgroup_destroy_locked().

 */

static void cgroup_offline_fn(struct work_struct *work)

static void cgroup_destroy_css_killed(struct cgroup *cgrp)

{

	struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);

	struct cgroup *parent = cgrp->parent;

	struct dentry *d = cgrp->dentry;

	struct cgroup_subsys *ss;



	mutex_lock(&cgroup_mutex);

	lockdep_assert_held(&cgroup_mutex);



	/*

	 * css_tryget() is guaranteed to fail now.  Tell subsystems to
@@ -4743,8 +4749,6 @@ static void cgroup_offline_fn(struct work_struct *work) 


	set_bit(CGRP_RELEASABLE, &parent->flags);

	check_for_release(parent);



	mutex_unlock(&cgroup_mutex);

}



static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)

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