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@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 0 insertions, 45 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ceeafe874b3f..dec62f5936ef 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1073,28 +1073,24 @@ 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) {
@@ -3917,37 +3913,6 @@ 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
@@ -4008,9 +3973,7 @@ 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);
@@ -4037,9 +4000,7 @@ 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:
@@ -4247,10 +4208,8 @@ 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);
 
@@ -4324,8 +4283,6 @@ 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
@@ -4452,8 +4409,6 @@ 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! */