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Message-Id: <1398373333-1521-7-git-send-email-tj@kernel.org>
Date: Thu, 24 Apr 2014 17:02:13 -0400
From: Tejun Heo <tj@...nel.org>
To: lizefan@...wei.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
hannes@...xchg.org, mhocko@...e.cz, nasa4836@...il.com,
Tejun Heo <tj@...nel.org>
Subject: [PATCH 6/6] 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: Tejun Heo <tj@...nel.org>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Jianyu Zhan <nasa4836@...il.com>
---
include/linux/cgroup.h | 9 ++++++++
kernel/cgroup.c | 59 ++++++++++++++++++++++++++++++++------------------
mm/memcontrol.c | 4 ++--
3 files changed, 49 insertions(+), 23 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 793f70a..2dfabb3 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -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.
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f1c98c5..a1a20e8 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1d0b297..c3f82f6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -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)
--
1.9.0
--
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