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Date: Mon, 04 Jun 2012 14:37:06 +0800
From: Li Zefan <lizefan@...wei.com>
To: Tejun Heo <tj@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Cgroups <cgroups@...r.kernel.org>
Subject: [PATCH] cgroup: remove hierarchy_mutex
It was introduced for memcg to iterate cgroup hierarchy without
holding cgroup_mutex, but soon after that it was replaced with
a lockless way in memcg.
No one used hierarchy_mutex since that, so remove it.
Signed-off-by: Li Zefan <lizefan@...wei.com>
---
Documentation/cgroups/cgroups.txt | 2 +-
include/linux/cgroup.h | 17 ++------------
kernel/cgroup.c | 45 -------------------------------------
3 files changed, 3 insertions(+), 61 deletions(-)
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 8e74980..e86faae 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -656,7 +656,7 @@ example in cpusets, no task may attach before 'cpus' and 'mems' are set
up.
void bind(struct cgroup *root)
-(cgroup_mutex and ss->hierarchy_mutex held by caller)
+(cgroup_mutex held by caller)
Called when a cgroup subsystem is rebound to a different hierarchy
and root cgroup. Currently this will only involve movement between
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index d3f5fba..c90eaa8 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -500,21 +500,8 @@ struct cgroup_subsys {
const char *name;
/*
- * Protects sibling/children links of cgroups in this
- * hierarchy, plus protects which hierarchy (or none) the
- * subsystem is a part of (i.e. root/sibling). To avoid
- * potential deadlocks, the following operations should not be
- * undertaken while holding any hierarchy_mutex:
- *
- * - allocating memory
- * - initiating hotplug events
- */
- struct mutex hierarchy_mutex;
- struct lock_class_key subsys_key;
-
- /*
* Link to parent, and list entry in parent's children.
- * Protected by this->hierarchy_mutex and cgroup_lock()
+ * Protected by cgroup_lock()
*/
struct cgroupfs_root *root;
struct list_head sibling;
@@ -602,7 +589,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
* the lifetime of cgroup_subsys_state is subsys's matter.
*
* Looking up and scanning function should be called under rcu_read_lock().
- * Taking cgroup_mutex()/hierarchy_mutex() is not necessary for following calls.
+ * Taking cgroup_mutex is not necessary for following calls.
* But the css returned by this routine can be "not populated yet" or "being
* destroyed". The caller should check css and cgroup's status.
*/
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0f3527d..907c3f2 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1063,28 +1063,24 @@ static int rebind_subsystems(struct cgroupfs_root *root,
BUG_ON(cgrp->subsys[i]);
BUG_ON(!dummytop->subsys[i]);
BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
- mutex_lock(&ss->hierarchy_mutex);
cgrp->subsys[i] = dummytop->subsys[i];
cgrp->subsys[i]->cgroup = cgrp;
list_move(&ss->sibling, &root->subsys_list);
ss->root = root;
if (ss->bind)
ss->bind(cgrp);
- mutex_unlock(&ss->hierarchy_mutex);
/* refcount was already taken, and we're keeping it */
} else if (bit & removed_bits) {
/* We're removing this subsystem */
BUG_ON(ss == NULL);
BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
- mutex_lock(&ss->hierarchy_mutex);
if (ss->bind)
ss->bind(dummytop);
dummytop->subsys[i]->cgroup = dummytop;
cgrp->subsys[i] = NULL;
subsys[i]->root = &rootnode;
list_move(&ss->sibling, &rootnode.subsys_list);
- mutex_unlock(&ss->hierarchy_mutex);
/* subsystem is now free - drop reference on module */
module_put(ss->module);
} else if (bit & final_bits) {
@@ -3906,37 +3902,6 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
set_bit(CSS_CLEAR_CSS_REFS, &css->flags);
}
-static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
-{
- /* We need to take each hierarchy_mutex in a consistent order */
- int i;
-
- /*
- * No worry about a race with rebind_subsystems that might mess up the
- * locking order, since both parties are under cgroup_mutex.
- */
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
- struct cgroup_subsys *ss = subsys[i];
- if (ss == NULL)
- continue;
- if (ss->root == root)
- mutex_lock(&ss->hierarchy_mutex);
- }
-}
-
-static void cgroup_unlock_hierarchy(struct cgroupfs_root *root)
-{
- int i;
-
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
- struct cgroup_subsys *ss = subsys[i];
- if (ss == NULL)
- continue;
- if (ss->root == root)
- mutex_unlock(&ss->hierarchy_mutex);
- }
-}
-
/*
* cgroup_create - create a cgroup
* @parent: cgroup that will be parent of the new cgroup
@@ -3997,9 +3962,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
ss->post_clone(cgrp);
}
- cgroup_lock_hierarchy(root);
list_add(&cgrp->sibling, &cgrp->parent->children);
- cgroup_unlock_hierarchy(root);
root->number_of_cgroups++;
err = cgroup_create_dir(cgrp, dentry, mode);
@@ -4026,9 +3989,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
err_remove:
- cgroup_lock_hierarchy(root);
list_del(&cgrp->sibling);
- cgroup_unlock_hierarchy(root);
root->number_of_cgroups--;
err_destroy:
@@ -4236,10 +4197,8 @@ again:
list_del_init(&cgrp->release_list);
raw_spin_unlock(&release_list_lock);
- cgroup_lock_hierarchy(cgrp->root);
/* delete this cgroup from parent->children */
list_del_init(&cgrp->sibling);
- cgroup_unlock_hierarchy(cgrp->root);
list_del_init(&cgrp->allcg_node);
@@ -4313,8 +4272,6 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
* need to invoke fork callbacks here. */
BUG_ON(!list_empty(&init_task.tasks));
- mutex_init(&ss->hierarchy_mutex);
- lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
ss->active = 1;
/* this function shouldn't be used with modular subsystems, since they
@@ -4441,8 +4398,6 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
}
write_unlock(&css_set_lock);
- mutex_init(&ss->hierarchy_mutex);
- lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
ss->active = 1;
/* success! */
--
1.7.9.7
--
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