Commit a2dd4247 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: make cgrp_dfl_root mountable 



cgrp_dfl_root will be used as the default unified hierarchy.  This
patch makes cgrp_dfl_root mountable by making the following changes.

* cgroup_init_early() now initializes cgrp_dfl_root w/
  CGRP_ROOT_SANE_BEHAVIOR.  The default hierarchy is always sane.

* parse_cgroupfs_options() and cgroup_mount() are updated such that
  cgrp_dfl_root is mounted if sane_behavior is specified w/o any
  subsystems.

* rebind_subsystems() now populates the root directory of
  cgrp_dfl_root.  Note that the function still guarantees success of
  rebinding subsystems to cgrp_dfl_root.  If populating fails while
  rebinding to cgrp_dfl_root, it whines but ignores the error.

* For backward compatibility, the default hierarchy shows up in
  /proc/$PID/cgroup only after it's explicitly mounted so that
  userland which doesn't make use of it doesn't see any change.

* "current_css_set_cg_links" file of debug cgroup now treats the
  default hierarchy the same as other hierarchies.  This is visible to
  userland.  Given that it's for debug controller, this should be
  fine.

* While at it, implement cgroup_on_dfl() which tests whether a give
  cgroup is on the default hierarchy or not.

The above changes make cgrp_dfl_root mostly equivalent to other
controllers but the actual unified hierarchy behaviors are not
implemented yet.  Let's plug child cgroup creation in cgrp_dfl_root
from create_cgroup() for now.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 4d3bb511

include/linux/cgroup.h

+10 −0
Original line number Diff line number Diff line
@@ -250,6 +250,9 @@ enum { 
	 *

	 * - "cgroup.clone_children" is removed.

	 *

	 * - If mount is requested with sane_behavior but without any

	 *   subsystem, the default unified hierarchy is mounted.

	 *

	 * - cpuset: tasks will be kept in empty cpusets when hotplug happens

	 *   and take masks of ancestors with non-empty cpus/mems, instead of

	 *   being moved to an ancestor.
@@ -468,6 +471,13 @@ struct cftype { 
#endif

};



extern struct cgroup_root cgrp_dfl_root;



static inline bool cgroup_on_dfl(const struct cgroup *cgrp)

{

	return cgrp->root == &cgrp_dfl_root;

}



/*

 * See the comment above CGRP_ROOT_SANE_BEHAVIOR for details.  This

 * function can be called as long as @cgrp is accessible.

kernel/cgroup.c

+61 −33
Original line number Diff line number Diff line
@@ -142,7 +142,13 @@ static const char *cgroup_subsys_name[] = { 
 * unattached - it never has more than a single cgroup, and all tasks are

 * part of that cgroup.

 */

static struct cgroup_root cgrp_dfl_root;

struct cgroup_root cgrp_dfl_root;



/*

 * The default hierarchy always exists but is hidden until mounted for the

 * first time.  This is for backward compatibility.

 */

static bool cgrp_dfl_root_visible;



/* The list of hierarchy roots */
@@ -999,10 +1005,22 @@ static int rebind_subsystems(struct cgroup_root *dst_root, 
			return -EBUSY;

	}



	if (dst_root != &cgrp_dfl_root) {

	ret = cgroup_populate_dir(&dst_root->cgrp, ss_mask);

		if (ret)

	if (ret) {

		if (dst_root != &cgrp_dfl_root)

			return ret;



		/*

		 * Rebinding back to the default root is not allowed to

		 * fail.  Using both default and non-default roots should

		 * be rare.  Moving subsystems back and forth even more so.

		 * Just warn about it and continue.

		 */

		if (cgrp_dfl_root_visible) {

			pr_warning("cgroup: failed to create files (%d) while rebinding 0x%lx to default root\n",

				   ret, ss_mask);

			pr_warning("cgroup: you may retry by moving them to a different hierarchy and unbinding\n");

		}

	}



	/*
@@ -1011,7 +1029,7 @@ static int rebind_subsystems(struct cgroup_root *dst_root, 
	 */

	mutex_unlock(&cgroup_mutex);

	for_each_subsys(ss, ssid)

		if ((ss_mask & (1 << ssid)) && ss->root != &cgrp_dfl_root)

		if (ss_mask & (1 << ssid))

			cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);

	mutex_lock(&cgroup_mutex);
@@ -1039,7 +1057,6 @@ static int rebind_subsystems(struct cgroup_root *dst_root, 
			ss->bind(css);

	}



	if (dst_root != &cgrp_dfl_root)

	kernfs_activate(dst_root->cgrp.kn);

	return 0;

}
@@ -1190,16 +1207,6 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) 
			return -ENOENT;

	}



	/*

	 * If the 'all' option was specified select all the subsystems,

	 * otherwise if 'none', 'name=' and a subsystem name options

	 * were not specified, let's default to 'all'

	 */

	if (all_ss || (!one_ss && !opts->none && !opts->name))

		for_each_subsys(ss, i)

			if (!ss->disabled)

				set_bit(i, &opts->subsys_mask);



	/* Consistency checks */



	if (opts->flags & CGRP_ROOT_SANE_BEHAVIOR) {
@@ -1211,6 +1218,23 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) 
			pr_err("cgroup: sane_behavior: noprefix, xattr, clone_children, release_agent and name are not allowed\n");

			return -EINVAL;

		}

	} else {

		/*

		 * If the 'all' option was specified select all the

		 * subsystems, otherwise if 'none', 'name=' and a subsystem

		 * name options were not specified, let's default to 'all'

		 */

		if (all_ss || (!one_ss && !opts->none && !opts->name))

			for_each_subsys(ss, i)

				if (!ss->disabled)

					set_bit(i, &opts->subsys_mask);



		/*

		 * We either have to specify by name or by subsystems. (So

		 * all empty hierarchies must have a name).

		 */

		if (!opts->subsys_mask && !opts->name)

			return -EINVAL;

	}



	/*
@@ -1226,13 +1250,6 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) 
	if (opts->subsys_mask && opts->none)

		return -EINVAL;



	/*

	 * We either have to specify by name or by subsystems. (So all

	 * empty hierarchies must have a name).

	 */

	if (!opts->subsys_mask && !opts->name)

		return -EINVAL;



	return 0;

}
@@ -1487,6 +1504,14 @@ retry: 
		goto out_unlock;



	/* look for a matching existing root */

	if (!opts.subsys_mask && !opts.none && !opts.name) {

		cgrp_dfl_root_visible = true;

		root = &cgrp_dfl_root;

		cgroup_get(&root->cgrp);

		ret = 0;

		goto out_unlock;

	}



	for_each_root(root) {

		bool name_match = false;
@@ -3622,6 +3647,13 @@ static long cgroup_create(struct cgroup *parent, const char *name, 
	struct cgroup_subsys *ss;

	struct kernfs_node *kn;



	/*

	 * XXX: The default hierarchy isn't fully implemented yet.  Block

	 * !root cgroup creation on it for now.

	 */

	if (root == &cgrp_dfl_root)

		return -EINVAL;



	/* allocate the cgroup and its ID, 0 is reserved for the root */

	cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);

	if (!cgrp)
@@ -4061,7 +4093,8 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) 
 */

int __init cgroup_init_early(void)

{

	static struct cgroup_sb_opts __initdata opts = { };

	static struct cgroup_sb_opts __initdata opts =

		{ .flags = CGRP_ROOT_SANE_BEHAVIOR };

	struct cgroup_subsys *ss;

	int i;
@@ -4198,7 +4231,7 @@ int proc_cgroup_show(struct seq_file *m, void *v) 
		struct cgroup *cgrp;

		int ssid, count = 0;



		if (root == &cgrp_dfl_root)

		if (root == &cgrp_dfl_root && !cgrp_dfl_root_visible)

			continue;



		seq_printf(m, "%d:", root->hierarchy_id);
@@ -4631,15 +4664,10 @@ static int current_css_set_cg_links_read(struct seq_file *seq, void *v) 
	cset = rcu_dereference(current->cgroups);

	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {

		struct cgroup *c = link->cgrp;

		const char *name = "?";



		if (c != &cgrp_dfl_root.cgrp) {

		cgroup_name(c, name_buf, NAME_MAX + 1);

			name = name_buf;

		}



		seq_printf(seq, "Root %d group %s\n",

			   c->root->hierarchy_id, name);

			   c->root->hierarchy_id, name_buf);

	}

	rcu_read_unlock();

	up_read(&css_set_rwsem);

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