Commit fa3ca07e authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: refactor hierarchy_id handling 



We're planning to converting hierarchy_ida to an idr and use it to
look up hierarchy from its id.  As we want the mapping to happen
atomically with cgroupfs_root registration, this patch refactors
hierarchy_id init / exit so that ida operations happen inside
cgroup_[root_]mutex.

* s/init_root_id()/cgroup_init_root_id()/ and make it return 0 or
  -errno like a normal function.

* Move hierarchy_id initialization from cgroup_root_from_opts() into
  cgroup_mount() block where the root is confirmed to be used and
  being registered while holding both mutexes.

* Split cgroup_drop_id() into cgroup_exit_root_id() and
  cgroup_free_root(), so that ID release can happen before dropping
  the mutexes in cgroup_kill_sb().  The latter expects hierarchy_id to
  be exited before being invoked.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent f722406f

kernel/cgroup.c

+35 −21
Original line number Diff line number Diff line
@@ -1426,13 +1426,13 @@ static void init_cgroup_root(struct cgroupfs_root *root) 
	list_add_tail(&cgrp->allcg_node, &root->allcg_list);

}



static bool init_root_id(struct cgroupfs_root *root)

static int cgroup_init_root_id(struct cgroupfs_root *root)

{

	int ret = 0;

	int ret;



	do {

		if (!ida_pre_get(&hierarchy_ida, GFP_KERNEL))

			return false;

			return -ENOMEM;

		spin_lock(&hierarchy_id_lock);

		/* Try to allocate the next unused ID */

		ret = ida_get_new_above(&hierarchy_ida, next_hierarchy_id,
@@ -1448,7 +1448,18 @@ static bool init_root_id(struct cgroupfs_root *root) 
		}

		spin_unlock(&hierarchy_id_lock);

	} while (ret);

	return true;

	return 0;

}



static void cgroup_exit_root_id(struct cgroupfs_root *root)

{

	if (root->hierarchy_id) {

		spin_lock(&hierarchy_id_lock);

		ida_remove(&hierarchy_ida, root->hierarchy_id);

		spin_unlock(&hierarchy_id_lock);



		root->hierarchy_id = 0;

	}

}



static int cgroup_test_super(struct super_block *sb, void *data)
@@ -1482,10 +1493,6 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts) 
	if (!root)

		return ERR_PTR(-ENOMEM);



	if (!init_root_id(root)) {

		kfree(root);

		return ERR_PTR(-ENOMEM);

	}

	init_cgroup_root(root);



	root->subsys_mask = opts->subsys_mask;
@@ -1500,18 +1507,16 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts) 
	return root;

}



static void cgroup_drop_root(struct cgroupfs_root *root)

static void cgroup_free_root(struct cgroupfs_root *root)

{

	if (!root)

		return;

	if (root) {

		/* hierarhcy ID shoulid already have been released */

		WARN_ON_ONCE(root->hierarchy_id);



	BUG_ON(!root->hierarchy_id);

	spin_lock(&hierarchy_id_lock);

	ida_remove(&hierarchy_ida, root->hierarchy_id);

	spin_unlock(&hierarchy_id_lock);

		ida_destroy(&root->cgroup_ida);

		kfree(root);

	}

}



static int cgroup_set_super(struct super_block *sb, void *data)

{
@@ -1597,7 +1602,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, 
	sb = sget(fs_type, cgroup_test_super, cgroup_set_super, 0, &opts);

	if (IS_ERR(sb)) {

		ret = PTR_ERR(sb);

		cgroup_drop_root(opts.new_root);

		cgroup_free_root(opts.new_root);

		goto drop_modules;

	}
@@ -1641,6 +1646,10 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, 
		if (ret)

			goto unlock_drop;



		ret = cgroup_init_root_id(root);

		if (ret)

			goto unlock_drop;



		ret = rebind_subsystems(root, root->subsys_mask);

		if (ret == -EBUSY) {

			free_cg_links(&tmp_cg_links);
@@ -1684,7 +1693,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, 
		 * We re-used an existing hierarchy - the new root (if

		 * any) is not needed

		 */

		cgroup_drop_root(opts.new_root);

		cgroup_free_root(opts.new_root);



		if (((root->flags | opts.flags) & CGRP_ROOT_SANE_BEHAVIOR) &&

		    root->flags != opts.flags) {
@@ -1702,6 +1711,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, 
	return dget(sb->s_root);



 unlock_drop:

	cgroup_exit_root_id(root);

	mutex_unlock(&cgroup_root_mutex);

	mutex_unlock(&cgroup_mutex);

	mutex_unlock(&inode->i_mutex);
@@ -1754,13 +1764,15 @@ static void cgroup_kill_sb(struct super_block *sb) { 
		root_count--;

	}



	cgroup_exit_root_id(root);



	mutex_unlock(&cgroup_root_mutex);

	mutex_unlock(&cgroup_mutex);



	simple_xattrs_free(&cgrp->xattrs);



	kill_litter_super(sb);

	cgroup_drop_root(root);

	cgroup_free_root(root);

}



static struct file_system_type cgroup_fs_type = {
@@ -4642,7 +4654,9 @@ int __init cgroup_init(void) 
	/* Add init_css_set to the hash table */

	key = css_set_hash(init_css_set.subsys);

	hash_add(css_set_table, &init_css_set.hlist, key);

	BUG_ON(!init_root_id(&rootnode));



	/* allocate id for the dummy hierarchy */

	BUG_ON(cgroup_init_root_id(&rootnode));



	cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);

	if (!cgroup_kobj) {

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