Commit 15a4c835 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup, memcg: implement css->id and convert css_from_id() to use it 



Until now, cgroup->id has been used to identify all the associated
csses and css_from_id() takes cgroup ID and returns the matching css
by looking up the cgroup and then dereferencing the css associated
with it; however, now that the lifetimes of cgroup and css are
separate, this is incorrect and breaks on the unified hierarchy when a
controller is disabled and enabled back again before the previous
instance is released.

This patch adds css->id which is a subsystem-unique ID and converts
css_from_id() to look up by the new css->id instead.  memcg is the
only user of css_from_id() and also converted to use css->id instead.

For traditional hierarchies, this shouldn't make any functional
difference.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jianyu Zhan <nasa4836@gmail.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent ddfcadab

include/linux/cgroup.h

+9 −0
Original line number Diff line number Diff line
@@ -62,6 +62,12 @@ struct cgroup_subsys_state { 
	/* the parent css */

	struct cgroup_subsys_state *parent;



	/*

	 * Subsys-unique ID.  0 is unused and root is always 1.  The

	 * matching css can be looked up using css_from_id().

	 */

	int id;



	unsigned int flags;



	/* percpu_ref killing and RCU release */
@@ -655,6 +661,9 @@ struct cgroup_subsys { 
	/* link to parent, protected by cgroup_lock() */

	struct cgroup_root *root;



	/* idr for css->id */

	struct idr css_idr;



	/*

	 * List of cftypes.  Each entry is the first entry of an array

	 * terminated by zero length name.

kernel/cgroup.c

+38 −21
Original line number Diff line number Diff line
@@ -100,8 +100,8 @@ static DECLARE_RWSEM(css_set_rwsem); 
#endif



/*

 * Protects cgroup_idr so that IDs can be released without grabbing

 * cgroup_mutex.

 * Protects cgroup_idr and css_idr so that IDs can be released without

 * grabbing cgroup_mutex.

 */

static DEFINE_SPINLOCK(cgroup_idr_lock);
@@ -1089,12 +1089,6 @@ static void cgroup_put(struct cgroup *cgrp) 
	if (WARN_ON_ONCE(cgrp->parent && !cgroup_is_dead(cgrp)))

		return;



	/*

	 * XXX: cgrp->id is only used to look up css's.  As cgroup and

	 * css's lifetimes will be decoupled, it should be made

	 * per-subsystem and moved to css->id so that lookups are

	 * successful until the target css is released.

	 */

	cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);

	cgrp->id = -1;
@@ -4104,8 +4098,11 @@ static void css_release(struct percpu_ref *ref) 
{

	struct cgroup_subsys_state *css =

		container_of(ref, struct cgroup_subsys_state, refcnt);

	struct cgroup_subsys *ss = css->ss;



	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);

	cgroup_idr_remove(&ss->css_idr, css->id);



	RCU_INIT_POINTER(css->cgroup->subsys[css->ss->id], NULL);

	call_rcu(&css->rcu_head, css_free_rcu_fn);

}
@@ -4195,9 +4192,17 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss) 
	if (err)

		goto err_free_css;



	err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_NOWAIT);

	if (err < 0)

		goto err_free_percpu_ref;

	css->id = err;



	err = cgroup_populate_dir(cgrp, 1 << ss->id);

	if (err)

		goto err_free_percpu_ref;

		goto err_free_id;



	/* @css is ready to be brought online now, make it visible */

	cgroup_idr_replace(&ss->css_idr, css, css->id);



	err = online_css(css);

	if (err)
@@ -4216,6 +4221,8 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss) 


err_clear_dir:

	cgroup_clear_dir(css->cgroup, 1 << css->ss->id);

err_free_id:

	cgroup_idr_remove(&ss->css_idr, css->id);

err_free_percpu_ref:

	percpu_ref_cancel_init(&css->refcnt);

err_free_css:
@@ -4642,7 +4649,7 @@ static struct kernfs_syscall_ops cgroup_kf_syscall_ops = { 
	.rename			= cgroup_rename,

};



static void __init cgroup_init_subsys(struct cgroup_subsys *ss)

static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)

{

	struct cgroup_subsys_state *css;
@@ -4651,6 +4658,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) 
	mutex_lock(&cgroup_tree_mutex);

	mutex_lock(&cgroup_mutex);



	idr_init(&ss->css_idr);

	INIT_LIST_HEAD(&ss->cfts);



	/* Create the root cgroup state for this subsystem */
@@ -4659,6 +4667,13 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) 
	/* We don't handle early failures gracefully */

	BUG_ON(IS_ERR(css));

	init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);

	if (early) {

		/* idr_alloc() can't be called safely during early init */

		css->id = 1;

	} else {

		css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);

		BUG_ON(css->id < 0);

	}



	/* Update the init_css_set to contain a subsys

	 * pointer to this state - since the subsystem is
@@ -4709,7 +4724,7 @@ int __init cgroup_init_early(void) 
		ss->name = cgroup_subsys_name[i];



		if (ss->early_init)

			cgroup_init_subsys(ss);

			cgroup_init_subsys(ss, true);

	}

	return 0;

}
@@ -4741,8 +4756,16 @@ int __init cgroup_init(void) 
	mutex_unlock(&cgroup_tree_mutex);



	for_each_subsys(ss, ssid) {

		if (!ss->early_init)

			cgroup_init_subsys(ss);

		if (ss->early_init) {

			struct cgroup_subsys_state *css =

				init_css_set.subsys[ss->id];



			css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,

						   GFP_KERNEL);

			BUG_ON(css->id < 0);

		} else {

			cgroup_init_subsys(ss, false);

		}



		list_add_tail(&init_css_set.e_cset_node[ssid],

			      &cgrp_dfl_root.cgrp.e_csets[ssid]);
@@ -5196,14 +5219,8 @@ struct cgroup_subsys_state *css_tryget_from_dir(struct dentry *dentry, 
 */

struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)

{

	struct cgroup *cgrp;



	WARN_ON_ONCE(!rcu_read_lock_held());



	cgrp = idr_find(&ss->root->cgroup_idr, id);

	if (cgrp)

		return cgroup_css(cgrp, ss);

	return NULL;

	return idr_find(&ss->css_idr, id);

}



#ifdef CONFIG_CGROUP_DEBUG

mm/memcontrol.c

+2 −2
Original line number Diff line number Diff line
@@ -527,7 +527,7 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) 


static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)

{

	return memcg->css.cgroup->id;

	return memcg->css.id;

}



static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
@@ -6401,7 +6401,7 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css) 
	struct mem_cgroup *memcg = mem_cgroup_from_css(css);

	struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(css));



	if (css->cgroup->id > MEM_CGROUP_ID_MAX)

	if (css->id > MEM_CGROUP_ID_MAX)

		return -ENOSPC;



	if (!parent)

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