[PATCH 8/8] cgroup: remove cgroup_tree_mutex
From: Tejun Heo
Date: Tue May 06 2014 - 16:20:00 EST
cgroup_tree_mutex was introduced to work around the circular
dependency between cgroup_mutex and kernfs active protection - some
kernfs file and directory operations needed cgroup_mutex putting
cgroup_mutex under active protection but cgroup also needs to be able
to access cgroup hierarchies and cftypes to determine which
kernfs_nodes need to be removed. cgroup_tree_mutex nested above both
cgroup_mutex and kernfs active protection and used to protect the
hierarchy and cftypes. While this worked, it added a lot of double
lockings and was generally cumbersome.
kernfs provides a mechanism to opt out of active protection and cgroup
was already using it for removal and subtree_control. There's no
reason to mix both methods of avoiding circular locking dependency and
the preceding cgroup_kn_lock_live() changes applied it to all relevant
cgroup kernfs operations making it unnecessary to nest cgroup_mutex
under kernfs active protection. The previous patch reversed the
original lock ordering and put cgroup_mutex above kernfs active
protection.
After these changes, all cgroup_tree_mutex usages are now accompanied
by cgroup_mutex making the former completely redundant. This patch
removes cgroup_tree_mutex and all its usages.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
kernel/cgroup.c | 64 ++++++++-------------------------------------------------
1 file changed, 9 insertions(+), 55 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 601a35d..4f218f3 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -71,15 +71,6 @@
MAX_CFTYPE_NAME + 2)
/*
- * cgroup_tree_mutex nests above cgroup_mutex and protects cftypes, file
- * creation/removal and hierarchy changing operations including cgroup
- * creation, removal, css association and controller rebinding. This outer
- * lock is needed mainly to resolve the circular dependency between kernfs
- * active ref and cgroup_mutex. cgroup_tree_mutex nests above both.
- */
-static DEFINE_MUTEX(cgroup_tree_mutex);
-
-/*
* cgroup_mutex is the master lock. Any modification to cgroup or its
* hierarchy must be performed while holding it.
*
@@ -111,11 +102,10 @@ static DEFINE_SPINLOCK(cgroup_idr_lock);
*/
static DEFINE_SPINLOCK(release_agent_path_lock);
-#define cgroup_assert_mutexes_or_rcu_locked() \
+#define cgroup_assert_mutex_or_rcu_locked() \
rcu_lockdep_assert(rcu_read_lock_held() || \
- lockdep_is_held(&cgroup_tree_mutex) || \
lockdep_is_held(&cgroup_mutex), \
- "cgroup_[tree_]mutex or RCU read lock required");
+ "cgroup_mutex or RCU read lock required");
/*
* cgroup destruction makes heavy use of work items and there can be a lot
@@ -243,7 +233,6 @@ static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
{
if (ss)
return rcu_dereference_check(cgrp->subsys[ss->id],
- lockdep_is_held(&cgroup_tree_mutex) ||
lockdep_is_held(&cgroup_mutex));
else
return &cgrp->dummy_css;
@@ -347,7 +336,6 @@ static int notify_on_release(const struct cgroup *cgrp)
for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++) \
if (!((css) = rcu_dereference_check( \
(cgrp)->subsys[(ssid)], \
- lockdep_is_held(&cgroup_tree_mutex) || \
lockdep_is_held(&cgroup_mutex)))) { } \
else
@@ -381,7 +369,7 @@ static int notify_on_release(const struct cgroup *cgrp)
/* iterate over child cgrps, lock should be held throughout iteration */
#define cgroup_for_each_live_child(child, cgrp) \
list_for_each_entry((child), &(cgrp)->children, sibling) \
- if (({ lockdep_assert_held(&cgroup_tree_mutex); \
+ if (({ lockdep_assert_held(&cgroup_mutex); \
cgroup_is_dead(child); })) \
; \
else
@@ -869,7 +857,6 @@ static void cgroup_destroy_root(struct cgroup_root *root)
struct cgroup *cgrp = &root->cgrp;
struct cgrp_cset_link *link, *tmp_link;
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
BUG_ON(atomic_read(&root->nr_cgrps));
@@ -899,7 +886,6 @@ static void cgroup_destroy_root(struct cgroup_root *root)
cgroup_exit_root_id(root);
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
kernfs_destroy_root(root->kf_root);
cgroup_free_root(root);
@@ -1096,7 +1082,6 @@ static void cgroup_kn_unlock(struct kernfs_node *kn)
cgrp = kn->parent->priv;
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
kernfs_unbreak_active_protection(kn);
cgroup_put(cgrp);
@@ -1135,7 +1120,6 @@ static struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn)
cgroup_get(cgrp);
kernfs_break_active_protection(kn);
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
if (!cgroup_is_dead(cgrp))
@@ -1149,7 +1133,6 @@ static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
{
char name[CGROUP_FILE_NAME_MAX];
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
}
@@ -1179,7 +1162,6 @@ static int rebind_subsystems(struct cgroup_root *dst_root, unsigned int ss_mask)
struct cgroup_subsys *ss;
int ssid, i, ret;
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
for_each_subsys(ss, ssid) {
@@ -1457,7 +1439,6 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
return -EINVAL;
}
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
/* See what subsystems are wanted */
@@ -1503,7 +1484,6 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
kfree(opts.release_agent);
kfree(opts.name);
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
return ret;
}
@@ -1606,7 +1586,6 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned int ss_mask)
struct css_set *cset;
int i, ret;
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_NOWAIT);
@@ -1696,7 +1675,6 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
if (!use_task_css_set_links)
cgroup_enable_task_cg_lists();
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
/* First find the desired set of subsystems */
@@ -1761,9 +1739,7 @@ retry:
*/
if (!atomic_inc_not_zero(&root->cgrp.refcnt)) {
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
msleep(10);
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
goto retry;
}
@@ -1796,7 +1772,6 @@ retry:
out_unlock:
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
kfree(opts.release_agent);
kfree(opts.name);
@@ -2507,7 +2482,6 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
struct css_set *src_cset;
int ret;
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
/* look up all csses currently attached to @cgrp's subtree */
@@ -2866,20 +2840,18 @@ static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
return -EPERM;
/*
- * We're gonna grab cgroup_tree_mutex which nests outside kernfs
+ * We're gonna grab cgroup_mutex which nests outside kernfs
* active_ref. kernfs_rename() doesn't require active_ref
- * protection. Break them before grabbing cgroup_tree_mutex.
+ * protection. Break them before grabbing cgroup_mutex.
*/
kernfs_break_active_protection(new_parent);
kernfs_break_active_protection(kn);
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
ret = kernfs_rename(kn, new_parent, new_name_str);
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
kernfs_unbreak_active_protection(kn);
kernfs_unbreak_active_protection(new_parent);
@@ -2944,7 +2916,6 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
struct cftype *cft;
int ret;
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
for (cft = cfts; cft->name[0] != '\0'; cft++) {
@@ -2980,7 +2951,6 @@ static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
struct cgroup_subsys_state *css;
int ret = 0;
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
/* add/rm files for all cgroups created before */
@@ -3049,7 +3019,6 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
static int cgroup_rm_cftypes_locked(struct cftype *cfts)
{
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
if (!cfts || !cfts[0].ss)
@@ -3076,11 +3045,9 @@ int cgroup_rm_cftypes(struct cftype *cfts)
{
int ret;
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
ret = cgroup_rm_cftypes_locked(cfts);
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
return ret;
}
@@ -3109,7 +3076,6 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
if (ret)
return ret;
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
list_add_tail(&cfts->node, &ss->cfts);
@@ -3118,7 +3084,6 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
cgroup_rm_cftypes_locked(cfts);
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
return ret;
}
@@ -3158,7 +3123,7 @@ css_next_child(struct cgroup_subsys_state *pos_css,
struct cgroup *cgrp = parent_css->cgroup;
struct cgroup *next;
- cgroup_assert_mutexes_or_rcu_locked();
+ cgroup_assert_mutex_or_rcu_locked();
/*
* @pos could already have been removed. Once a cgroup is removed,
@@ -3224,7 +3189,7 @@ css_next_descendant_pre(struct cgroup_subsys_state *pos,
{
struct cgroup_subsys_state *next;
- cgroup_assert_mutexes_or_rcu_locked();
+ cgroup_assert_mutex_or_rcu_locked();
/* if first iteration, visit @root */
if (!pos)
@@ -3264,7 +3229,7 @@ css_rightmost_descendant(struct cgroup_subsys_state *pos)
{
struct cgroup_subsys_state *last, *tmp;
- cgroup_assert_mutexes_or_rcu_locked();
+ cgroup_assert_mutex_or_rcu_locked();
do {
last = pos;
@@ -3311,7 +3276,7 @@ css_next_descendant_post(struct cgroup_subsys_state *pos,
{
struct cgroup_subsys_state *next;
- cgroup_assert_mutexes_or_rcu_locked();
+ cgroup_assert_mutex_or_rcu_locked();
/* if first iteration, visit leftmost descendant which may be @root */
if (!pos)
@@ -4179,7 +4144,6 @@ static int online_css(struct cgroup_subsys_state *css)
struct cgroup_subsys *ss = css->ss;
int ret = 0;
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
if (ss->css_online)
@@ -4197,7 +4161,6 @@ static void offline_css(struct cgroup_subsys_state *css)
{
struct cgroup_subsys *ss = css->ss;
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
if (!(css->flags & CSS_ONLINE))
@@ -4400,7 +4363,6 @@ static void css_killed_work_fn(struct work_struct *work)
container_of(work, struct cgroup_subsys_state, destroy_work);
struct cgroup *cgrp = css->cgroup;
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
/*
@@ -4418,7 +4380,6 @@ static void css_killed_work_fn(struct work_struct *work)
cgroup_destroy_css_killed(cgrp);
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
/*
* Put the css refs from kill_css(). Each css holds an extra
@@ -4451,7 +4412,6 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
*/
static void kill_css(struct cgroup_subsys_state *css)
{
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
/*
@@ -4511,7 +4471,6 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
bool empty;
int ssid;
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
/*
@@ -4594,7 +4553,6 @@ static void cgroup_destroy_css_killed(struct cgroup *cgrp)
{
struct cgroup *parent = cgrp->parent;
- lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
/* delete this cgroup from parent->children */
@@ -4648,7 +4606,6 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
idr_init(&ss->css_idr);
@@ -4686,7 +4643,6 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
cgrp_dfl_root.subsys_mask |= 1 << ss->id;
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
}
/**
@@ -4736,7 +4692,6 @@ int __init cgroup_init(void)
BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
- mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
/* Add init_css_set to the hash table */
@@ -4746,7 +4701,6 @@ int __init cgroup_init(void)
BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
mutex_unlock(&cgroup_mutex);
- mutex_unlock(&cgroup_tree_mutex);
for_each_subsys(ss, ssid) {
if (ss->early_init) {
--
1.9.0
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