[PATCHSET cgroup/for-3.15] cgroup: prepare for the default unified hierarchy

[PATCHSET cgroup/for-3.15] cgroup: prepare for the default unified hierarchy

[Tejun Heo]

Hello,

The planned unified hierarchy is just around the corner.  We're gonna
repurpose the dummy hierarchy to serve as the default unified
hierarchy.  Controllers which aren't attached to other hierarchies are
already automatically bound to the dummy hierarchy; however, the dummy
hierarchy is minimally initialized during boot and can't currently act
as a full hierarchy.

This patchset gradually turns the dummy hierarchy into fully
functional default one and makes it mountable via selecting
sane_behavior without any subsystems specified.  While this patchset
does make the default hierarchy mountable, the unified hierarchy
functionality isn't implemented yet and cgroup creation in the default
hierarchy is rejected for now.

This lays down all the boilerplate work for the unified hierarchy.
The next patchset will implement the actual unified functionality.

This patchset contains the following eleven patches.

 0001-cgroup-cgroup-subsys-should-be-cleared-after-the-css.patch
 0002-cgroup-relocate-setting-of-CGRP_DEAD.patch
 0003-cgroup-reorganize-cgroup-bootstrapping.patch
 0004-cgroup-use-cgroup_setup_root-to-initialize-cgroup_du.patch
 0005-cgroup-remove-NULL-checks-from-pr_cont_-cgroup_-name.patch
 0006-cgroup-treat-cgroup_dummy_root-as-an-equivalent-hier.patch
 0007-cgroup-move-subsys_mask-from-cgroupfs_root-to-cgroup.patch
 0008-cgroup-rename-cgroup_dummy_root-and-related-names.patch
 0009-cgroup-drop-const-from-buffer-of-cftype-write_string.patch
 0010-cgroup-make-cgrp_dfl_root-mountable.patch
 0011-cgroup-implement-CFTYPE_ONLY_ON_DFL.patch

0001-0002 are misc fix / prep.

0003-0009 (mostly) turn the dummy hierarchy into a full hierarchy
which takes on controllers which aren't attached to other hierarchies.

0010-0011 make the default hierarchy mountable and implement
CFTYPE_ONLY_DFL.

This patchset is on top of cgroup/for-3.15 b8dadcb58d54 ("cpuset: use
rcu_read_lock() to protect task_cs()").  diffstat follows.

 block/blk-throttle.c      |    4
 block/cfq-iosched.c       |    4
 include/linux/cgroup.h    |   57 ++---
 kernel/cgroup.c           |  464 +++++++++++++++++++++++++---------------------
 kernel/cgroup_freezer.c   |    2
 kernel/cpuset.c           |    2
 mm/hugetlb_cgroup.c       |    2
 mm/memcontrol.c           |    4
 net/core/netprio_cgroup.c |    2
 net/ipv4/tcp_memcontrol.c |    2
 security/device_cgroup.c  |    4
 11 files changed, 295 insertions(+), 252 deletions(-)

Thanks.

--
tejun

[PATCH 01/11] cgroup: cgroup->subsys[] should be cleared after the css is offlined

[Tejun Heo]

After a css finishes offlining, offline_css() mistakenly performs
RCU_INIT_POINTER(css->cgroup->subsys[ss->id], css) which just sets the
cgroup->subsys[] pointer to the current value.  The intention was to
clear it after offline is complete, not reassign the same value.

Update it to assign NULL instead of the current value.  This makes
cgroup_css() to return NULL once offline is complete.  All the
existing users of the function either can handle NULL return already
or guarantee that the css doesn't get offlined.

While this is a bugfix, as css lifetime is currently tied to the
cgroup it belongs to, this bug doesn't cause any actual problems.

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 kernel/cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 306ad0e..ca19735 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3535,7 +3535,7 @@ static void offline_css(struct cgroup_subsys_state *css)
 
 	css->flags &= ~CSS_ONLINE;
 	css->cgroup->nr_css--;
-	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], css);
+	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
 }
 
 /**
-- 
1.8.5.3

[PATCH 02/11] cgroup: relocate setting of CGRP_DEAD

[Tejun Heo]

In cgroup_destroy_locked(), move setting of CGRP_DEAD above
invocations of kill_css().  This doesn't make any visible behavior
difference now but will be used to inhibit manipulating controller
enable states of a dying cgroup on the unified hierarchy.

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 kernel/cgroup.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ca19735..7bf1459 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3868,6 +3868,15 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 		return -EBUSY;
 
 	/*
+	 * Mark @cgrp dead.  This prevents further task migration and child
+	 * creation by disabling cgroup_lock_live_group().  Note that
+	 * CGRP_DEAD assertion is depended upon by css_next_child() to
+	 * resume iteration after dropping RCU read lock.  See
+	 * css_next_child() for details.
+	 */
+	set_bit(CGRP_DEAD, &cgrp->flags);
+
+	/*
 	 * Initiate massacre of all css's.  cgroup_destroy_css_killed()
 	 * will be invoked to perform the rest of destruction once the
 	 * percpu refs of all css's are confirmed to be killed.  This
@@ -3878,15 +3887,6 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 		kill_css(css);
 	mutex_lock(&cgroup_mutex);
 
-	/*
-	 * Mark @cgrp dead.  This prevents further task migration and child
-	 * creation by disabling cgroup_lock_live_group().  Note that
-	 * CGRP_DEAD assertion is depended upon by css_next_child() to
-	 * resume iteration after dropping RCU read lock.  See
-	 * css_next_child() for details.
-	 */
-	set_bit(CGRP_DEAD, &cgrp->flags);
-
 	/* CGRP_DEAD is set, remove from ->release_list for the last time */
 	raw_spin_lock(&release_list_lock);
 	if (!list_empty(&cgrp->release_list))
-- 
1.8.5.3

[PATCH 03/11] cgroup: reorganize cgroup bootstrapping

[Tejun Heo]

* Fields of init_css_set and css_set_count are now set using
  initializer instead of programmatically from cgroup_init_early().

* init_cgroup_root() now also takes @opts and performs the optional
  part of initialization too.  The leftover part of
  cgroup_root_from_opts() is collapsed into its only caller -
  cgroup_mount().

* Initialization of cgroup_root_count and linking of init_css_set are
  moved from cgroup_init_early() to to cgroup_init().  None of the
  early_init users depends on init_css_set being linked.

* Subsystem initializations are moved after dummy hierarchy init and
  init_css_set linking.

These changes reorganize the bootstrap logic so that the dummy
hierarchy can share the usual hierarchy init path and be made more
normal.  These changes don't make noticeable behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/cgroup.c | 100 +++++++++++++++++++++++++++-----------------------------
 1 file changed, 49 insertions(+), 51 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7bf1459..12a0bda 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -338,16 +338,24 @@ struct cgrp_cset_link {
 	struct list_head	cgrp_link;
 };
 
-/* The default css_set - used by init and its children prior to any
+/*
+ * The default css_set - used by init and its children prior to any
  * hierarchies being mounted. It contains a pointer to the root state
  * for each subsystem. Also used to anchor the list of css_sets. Not
  * reference-counted, to improve performance when child cgroups
  * haven't been created.
  */
+static struct css_set init_css_set = {
+	.refcount		= ATOMIC_INIT(1),
+	.cgrp_links		= LIST_HEAD_INIT(init_css_set.cgrp_links),
+	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),
+	.mg_tasks		= LIST_HEAD_INIT(init_css_set.mg_tasks),
+	.mg_preload_node	= LIST_HEAD_INIT(init_css_set.mg_preload_node),
+	.mg_node		= LIST_HEAD_INIT(init_css_set.mg_node),
+};
 
-static struct css_set init_css_set;
 static struct cgrp_cset_link init_cgrp_cset_link;
-static int css_set_count;
+static int css_set_count	= 1;	/* 1 for init_css_set */
 
 /*
  * hash table for cgroup groups. This improves the performance to find
@@ -1352,7 +1360,8 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
 	cgrp->dummy_css.cgroup = cgrp;
 }
 
-static void init_cgroup_root(struct cgroupfs_root *root)
+static void init_cgroup_root(struct cgroupfs_root *root,
+			     struct cgroup_sb_opts *opts)
 {
 	struct cgroup *cgrp = &root->top_cgroup;
 
@@ -1361,20 +1370,6 @@ static void init_cgroup_root(struct cgroupfs_root *root)
 	cgrp->root = root;
 	init_cgroup_housekeeping(cgrp);
 	idr_init(&root->cgroup_idr);
-}
-
-static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
-{
-	struct cgroupfs_root *root;
-
-	if (!opts->subsys_mask && !opts->none)
-		return ERR_PTR(-EINVAL);
-
-	root = kzalloc(sizeof(*root), GFP_KERNEL);
-	if (!root)
-		return ERR_PTR(-ENOMEM);
-
-	init_cgroup_root(root);
 
 	root->flags = opts->flags;
 	if (opts->release_agent)
@@ -1383,7 +1378,6 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
 		strcpy(root->name, opts->name);
 	if (opts->cpuset_clone_children)
 		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags);
-	return root;
 }
 
 static int cgroup_setup_root(struct cgroupfs_root *root, unsigned long ss_mask)
@@ -1548,13 +1542,24 @@ retry:
 		goto out_unlock;
 	}
 
-	/* no such thing, create a new one */
-	root = cgroup_root_from_opts(&opts);
-	if (IS_ERR(root)) {
-		ret = PTR_ERR(root);
+	/*
+	 * No such thing, create a new one.  name= matching without subsys
+	 * specification is allowed for already existing hierarchies but we
+	 * can't create new one without subsys specification.
+	 */
+	if (!opts.subsys_mask && !opts.none) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	root = kzalloc(sizeof(*root), GFP_KERNEL);
+	if (!root) {
+		ret = -ENOMEM;
 		goto out_unlock;
 	}
 
+	init_cgroup_root(root, &opts);
+
 	ret = cgroup_setup_root(root, opts.subsys_mask);
 	if (ret)
 		cgroup_free_root(root);
@@ -4030,26 +4035,13 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
  */
 int __init cgroup_init_early(void)
 {
+	static struct cgroup_sb_opts __initdata opts = { };
 	struct cgroup_subsys *ss;
 	int i;
 
-	atomic_set(&init_css_set.refcount, 1);
-	INIT_LIST_HEAD(&init_css_set.cgrp_links);
-	INIT_LIST_HEAD(&init_css_set.tasks);
-	INIT_LIST_HEAD(&init_css_set.mg_tasks);
-	INIT_LIST_HEAD(&init_css_set.mg_preload_node);
-	INIT_LIST_HEAD(&init_css_set.mg_node);
-	INIT_HLIST_NODE(&init_css_set.hlist);
-	css_set_count = 1;
-	init_cgroup_root(&cgroup_dummy_root);
-	cgroup_root_count = 1;
+	init_cgroup_root(&cgroup_dummy_root, &opts);
 	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
 
-	init_cgrp_cset_link.cset = &init_css_set;
-	init_cgrp_cset_link.cgrp = cgroup_dummy_top;
-	list_add(&init_cgrp_cset_link.cset_link, &cgroup_dummy_top->cset_links);
-	list_add(&init_cgrp_cset_link.cgrp_link, &init_css_set.cgrp_links);
-
 	for_each_subsys(ss, i) {
 		WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
 		     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p name:id=%d:%s\n",
@@ -4077,22 +4069,10 @@ int __init cgroup_init(void)
 {
 	struct cgroup_subsys *ss;
 	unsigned long key;
-	int i, err;
+	int ssid, err;
 
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
 
-	for_each_subsys(ss, i) {
-		if (!ss->early_init)
-			cgroup_init_subsys(ss);
-
-		/*
-		 * cftype registration needs kmalloc and can't be done
-		 * during early_init.  Register base cftypes separately.
-		 */
-		if (ss->base_cftypes)
-			WARN_ON(cgroup_add_cftypes(ss, ss->base_cftypes));
-	}
-
 	/* allocate id for the dummy hierarchy */
 	mutex_lock(&cgroup_mutex);
 
@@ -4106,8 +4086,26 @@ int __init cgroup_init(void)
 			0, 1, GFP_KERNEL);
 	BUG_ON(err < 0);
 
+	cgroup_root_count = 1;
+	init_cgrp_cset_link.cset = &init_css_set;
+	init_cgrp_cset_link.cgrp = cgroup_dummy_top;
+	list_add(&init_cgrp_cset_link.cset_link, &cgroup_dummy_top->cset_links);
+	list_add(&init_cgrp_cset_link.cgrp_link, &init_css_set.cgrp_links);
+
 	mutex_unlock(&cgroup_mutex);
 
+	for_each_subsys(ss, ssid) {
+		if (!ss->early_init)
+			cgroup_init_subsys(ss);
+
+		/*
+		 * cftype registration needs kmalloc and can't be done
+		 * during early_init.  Register base cftypes separately.
+		 */
+		if (ss->base_cftypes)
+			WARN_ON(cgroup_add_cftypes(ss, ss->base_cftypes));
+	}
+
 	cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
 	if (!cgroup_kobj)
 		return -ENOMEM;
-- 
1.8.5.3

[PATCH 04/11] cgroup: use cgroup_setup_root() to initialize cgroup_dummy_root

[Tejun Heo]

cgroup_dummy_root is used to host controllers which aren't attached to
any other hierarchy.  The root is minimally set up during kernfs
bootstrap and didn't go through full hierarchy initialization.  We're
planning to use cgroup_dummy_root for the default unified hierarchy
and thus want it to be fully functional.

Replace the special initialization, which was collected into
cgroup_init() by the previous patch, with an invocation of
cgroup_setup_root().  This simplifies the init path and makes
cgroup_dummy_root a full hierarchy with its own kernfs_root and all.

As this puts the dummy hierarchy on the cgroup_roots list, rename
for_each_active_root() to for_each_root() and update its users to skip
the dummy root for now.

This patch doesn't cause any userland visible behavior changes at this
point.

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 kernel/cgroup.c | 43 ++++++++++++++++++++-----------------------
 1 file changed, 20 insertions(+), 23 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 12a0bda..2483f4e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -289,8 +289,8 @@ static int notify_on_release(const struct cgroup *cgrp)
 	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&		\
 	     (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
 
-/* iterate across the active hierarchies */
-#define for_each_active_root(root)					\
+/* iterate across the hierarchies */
+#define for_each_root(root)						\
 	list_for_each_entry((root), &cgroup_roots, root_list)
 
 /**
@@ -354,7 +354,6 @@ static struct css_set init_css_set = {
 	.mg_node		= LIST_HEAD_INIT(init_css_set.mg_node),
 };
 
-static struct cgrp_cset_link init_cgrp_cset_link;
 static int css_set_count	= 1;	/* 1 for init_css_set */
 
 /*
@@ -693,14 +692,13 @@ static struct cgroupfs_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
 	return top_cgrp->root;
 }
 
-static int cgroup_init_root_id(struct cgroupfs_root *root, int start, int end)
+static int cgroup_init_root_id(struct cgroupfs_root *root)
 {
 	int id;
 
 	lockdep_assert_held(&cgroup_mutex);
 
-	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, start, end,
-			      GFP_KERNEL);
+	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
 	if (id < 0)
 		return id;
 
@@ -1405,8 +1403,7 @@ static int cgroup_setup_root(struct cgroupfs_root *root, unsigned long ss_mask)
 	if (ret)
 		goto out;
 
-	/* ID 0 is reserved for dummy root, 1 for unified hierarchy */
-	ret = cgroup_init_root_id(root, 2, 0);
+	ret = cgroup_init_root_id(root);
 	if (ret)
 		goto out;
 
@@ -1486,9 +1483,12 @@ retry:
 		goto out_unlock;
 
 	/* look for a matching existing root */
-	for_each_active_root(root) {
+	for_each_root(root) {
 		bool name_match = false;
 
+		if (root == &cgroup_dummy_root)
+			continue;
+
 		/*
 		 * If we asked for a name then it must match.  Also, if
 		 * name matches but sybsys_mask doesn't, we should fail.
@@ -2106,9 +2106,12 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 	int retval = 0;
 
 	mutex_lock(&cgroup_mutex);
-	for_each_active_root(root) {
+	for_each_root(root) {
 		struct cgroup *from_cgrp;
 
+		if (root == &cgroup_dummy_root)
+			continue;
+
 		down_read(&css_set_rwsem);
 		from_cgrp = task_cgroup_from_root(from, root);
 		up_read(&css_set_rwsem);
@@ -4073,26 +4076,17 @@ int __init cgroup_init(void)
 
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
 
-	/* allocate id for the dummy hierarchy */
+	mutex_lock(&cgroup_tree_mutex);
 	mutex_lock(&cgroup_mutex);
 
 	/* 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(cgroup_init_root_id(&cgroup_dummy_root, 0, 1));
-
-	err = idr_alloc(&cgroup_dummy_root.cgroup_idr, cgroup_dummy_top,
-			0, 1, GFP_KERNEL);
-	BUG_ON(err < 0);
-
-	cgroup_root_count = 1;
-	init_cgrp_cset_link.cset = &init_css_set;
-	init_cgrp_cset_link.cgrp = cgroup_dummy_top;
-	list_add(&init_cgrp_cset_link.cset_link, &cgroup_dummy_top->cset_links);
-	list_add(&init_cgrp_cset_link.cgrp_link, &init_css_set.cgrp_links);
+	BUG_ON(cgroup_setup_root(&cgroup_dummy_root, 0));
 
 	mutex_unlock(&cgroup_mutex);
+	mutex_unlock(&cgroup_tree_mutex);
 
 	for_each_subsys(ss, ssid) {
 		if (!ss->early_init)
@@ -4176,11 +4170,14 @@ int proc_cgroup_show(struct seq_file *m, void *v)
 	mutex_lock(&cgroup_mutex);
 	down_read(&css_set_rwsem);
 
-	for_each_active_root(root) {
+	for_each_root(root) {
 		struct cgroup_subsys *ss;
 		struct cgroup *cgrp;
 		int ssid, count = 0;
 
+		if (root == &cgroup_dummy_root)
+			continue;
+
 		seq_printf(m, "%d:", root->hierarchy_id);
 		for_each_subsys(ss, ssid)
 			if (root->subsys_mask & (1 << ssid))
-- 
1.8.5.3

[PATCH 05/11] cgroup: remove NULL checks from [pr_cont_]cgroup_{name|path}()

[Tejun Heo]

The dummy hierarchy is now a fully functional one and dummy_top has a
kernfs_node associated with it.  Drop the NULL checks in
[pr_cont_]cont_{name|path}() which are no longer necessary.

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 include/linux/cgroup.h | 24 ++++--------------------
 1 file changed, 4 insertions(+), 20 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index acbb9a4..9f4f253 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -508,39 +508,23 @@ struct cgroup_subsys_state *seq_css(struct seq_file *seq);
 
 static inline int cgroup_name(struct cgroup *cgrp, char *buf, size_t buflen)
 {
-	/* dummy_top doesn't have a kn associated */
-	if (cgrp->kn)
-		return kernfs_name(cgrp->kn, buf, buflen);
-	else
-		return strlcpy(buf, "/", buflen);
+	return kernfs_name(cgrp->kn, buf, buflen);
 }
 
 static inline char * __must_check cgroup_path(struct cgroup *cgrp, char *buf,
 					      size_t buflen)
 {
-	/* dummy_top doesn't have a kn associated */
-	if (cgrp->kn)
-		return kernfs_path(cgrp->kn, buf, buflen);
-	strlcpy(buf, "/", buflen);
-	return (buflen <= 2) ? NULL : buf;
+	return kernfs_path(cgrp->kn, buf, buflen);
 }
 
 static inline void pr_cont_cgroup_name(struct cgroup *cgrp)
 {
-	/* dummy_top doesn't have a kn associated */
-	if (cgrp->kn)
-		pr_cont_kernfs_name(cgrp->kn);
-	else
-		pr_cont("/");
+	pr_cont_kernfs_name(cgrp->kn);
 }
 
 static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
 {
-	/* dummy_top doesn't have a kn associated */
-	if (cgrp->kn)
-		pr_cont_kernfs_path(cgrp->kn);
-	else
-		pr_cont("/");
+	pr_cont_kernfs_path(cgrp->kn);
 }
 
 char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
-- 
1.8.5.3

[PATCH 06/11] cgroup: treat cgroup_dummy_root as an equivalent hierarchy during rebinding

[Tejun Heo]

Currently, while rebinding, cgroup_dummy_root serves as the anchor
point.  In addition to the target root, rebind_subsystems() takes
@added_mask and @removed_mask.  The subsystems specified in the former
are expected to be on the dummy root and then moved to the target
root.  The ones in the latter are moved from non-dummy root to dummy.
Now that the dummy root is a fully functional one and we're planning
to use it for the default unified hierarchy, this level of distinction
between dummy and non-dummy roots is quite awkward.

This patch updates rebind_subsystems() to take the target root and one
subsystem mask and move the specified subsystmes to the target root
which may or may not be the dummy root.  IOW, unbinding now becomes
moving the subsystems to the dummy root and binding to non-dummy root.
This makes the dummy root mostly equivalent to other hierarchies in
terms of the mechanism of moving subsystems around; however, we still
retain all the semantical restrictions so that this patch doesn't
introduce any visible behavior differences.  Another noteworthy detail
is that rebind_subsystems() guarantees that moving a subsystem to the
dummy root never fails so that valid unmounting attempts always
succeed.

This unifies binding and unbinding of subsystems.  The invocation
points of ->bind() were inconsistent between the two and now moved
after whole rebinding is complete.  This doesn't break the current
users and generally makes more sense.

All rebind_subsystems() users are converted accordingly.  Note that
cgroup_remount() now makes two calls to rebind_subsystems() to bind
and then unbind the requested subsystems.

This will allow repurposing of the dummy hierarchy as the default
unified hierarchy and shouldn't make any userland visible behavior
difference.

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 kernel/cgroup.c | 100 +++++++++++++++++++++++++++++++-------------------------
 1 file changed, 56 insertions(+), 44 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2483f4e..9b9a294 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -175,8 +175,8 @@ static int need_forkexit_callback __read_mostly;
 static struct cftype cgroup_base_files[];
 
 static void cgroup_put(struct cgroup *cgrp);
-static int rebind_subsystems(struct cgroupfs_root *root,
-			     unsigned long added_mask, unsigned removed_mask);
+static int rebind_subsystems(struct cgroupfs_root *dst_root,
+			     unsigned long ss_mask);
 static void cgroup_destroy_css_killed(struct cgroup *cgrp);
 static int cgroup_destroy_locked(struct cgroup *cgrp);
 static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
@@ -739,7 +739,7 @@ static void cgroup_destroy_root(struct cgroupfs_root *root)
 	BUG_ON(!list_empty(&cgrp->children));
 
 	/* Rebind all subsystems back to the default hierarchy */
-	WARN_ON(rebind_subsystems(root, 0, root->subsys_mask));
+	rebind_subsystems(&cgroup_dummy_root, root->subsys_mask);
 
 	/*
 	 * Release all the links from cset_links to this hierarchy's
@@ -976,69 +976,77 @@ static void cgroup_clear_dir(struct cgroup *cgrp, unsigned long subsys_mask)
 	}
 }
 
-static int rebind_subsystems(struct cgroupfs_root *root,
-			     unsigned long added_mask, unsigned removed_mask)
+static int rebind_subsystems(struct cgroupfs_root *dst_root,
+			     unsigned long ss_mask)
 {
-	struct cgroup *cgrp = &root->top_cgroup;
+	struct cgroup *dst_top = &dst_root->top_cgroup;
 	struct cgroup_subsys *ss;
-	int i, ret;
+	int ssid, ret;
 
 	lockdep_assert_held(&cgroup_tree_mutex);
 	lockdep_assert_held(&cgroup_mutex);
 
-	/* Check that any added subsystems are currently free */
-	for_each_subsys(ss, i)
-		if ((added_mask & (1 << i)) && ss->root != &cgroup_dummy_root)
+	for_each_subsys(ss, ssid) {
+		if (!(ss_mask & (1 << ssid)))
+			continue;
+
+		/* if @ss is on the dummy_root, we can always move it */
+		if (ss->root == &cgroup_dummy_root)
+			continue;
+
+		/* if @ss has non-root cgroups attached to it, can't move */
+		if (!list_empty(&ss->root->top_cgroup.children))
 			return -EBUSY;
 
-	ret = cgroup_populate_dir(cgrp, added_mask);
-	if (ret)
-		return ret;
+		/* can't move between two non-dummy roots either */
+		if (dst_root != &cgroup_dummy_root)
+			return -EBUSY;
+	}
+
+	if (dst_root != &cgroup_dummy_root) {
+		ret = cgroup_populate_dir(dst_top, ss_mask);
+		if (ret)
+			return ret;
+	}
 
 	/*
 	 * Nothing can fail from this point on.  Remove files for the
 	 * removed subsystems and rebind each subsystem.
 	 */
 	mutex_unlock(&cgroup_mutex);
-	cgroup_clear_dir(cgrp, removed_mask);
+	for_each_subsys(ss, ssid)
+		if ((ss_mask & (1 << ssid)) && ss->root != &cgroup_dummy_root)
+			cgroup_clear_dir(&ss->root->top_cgroup, 1 << ssid);
 	mutex_lock(&cgroup_mutex);
 
-	for_each_subsys(ss, i) {
-		unsigned long bit = 1UL << i;
-
-		if (bit & added_mask) {
-			/* We're binding this subsystem to this hierarchy */
-			BUG_ON(cgroup_css(cgrp, ss));
-			BUG_ON(!cgroup_css(cgroup_dummy_top, ss));
-			BUG_ON(cgroup_css(cgroup_dummy_top, ss)->cgroup != cgroup_dummy_top);
+	for_each_subsys(ss, ssid) {
+		struct cgroupfs_root *src_root;
+		struct cgroup *src_top;
+		struct cgroup_subsys_state *css;
 
-			rcu_assign_pointer(cgrp->subsys[i],
-					   cgroup_css(cgroup_dummy_top, ss));
-			cgroup_css(cgrp, ss)->cgroup = cgrp;
+		if (!(ss_mask & (1 << ssid)))
+			continue;
 
-			ss->root = root;
-			if (ss->bind)
-				ss->bind(cgroup_css(cgrp, ss));
+		src_root = ss->root;
+		src_top = &src_root->top_cgroup;
+		css = cgroup_css(src_top, ss);
 
-			/* refcount was already taken, and we're keeping it */
-			root->subsys_mask |= bit;
-		} else if (bit & removed_mask) {
-			/* We're removing this subsystem */
-			BUG_ON(cgroup_css(cgrp, ss) != cgroup_css(cgroup_dummy_top, ss));
-			BUG_ON(cgroup_css(cgrp, ss)->cgroup != cgrp);
+		WARN_ON(!css || cgroup_css(dst_top, ss));
 
-			if (ss->bind)
-				ss->bind(cgroup_css(cgroup_dummy_top, ss));
+		RCU_INIT_POINTER(src_top->subsys[ssid], NULL);
+		rcu_assign_pointer(dst_top->subsys[ssid], css);
+		ss->root = dst_root;
+		css->cgroup = dst_top;
 
-			cgroup_css(cgroup_dummy_top, ss)->cgroup = cgroup_dummy_top;
-			RCU_INIT_POINTER(cgrp->subsys[i], NULL);
+		src_root->subsys_mask &= ~(1 << ssid);
+		dst_root->subsys_mask |= 1 << ssid;
 
-			cgroup_subsys[i]->root = &cgroup_dummy_root;
-			root->subsys_mask &= ~bit;
-		}
+		if (ss->bind)
+			ss->bind(css);
 	}
 
-	kernfs_activate(cgrp->kn);
+	if (dst_root != &cgroup_dummy_root)
+		kernfs_activate(dst_top->kn);
 	return 0;
 }
 
@@ -1277,10 +1285,12 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
 		goto out_unlock;
 	}
 
-	ret = rebind_subsystems(root, added_mask, removed_mask);
+	ret = rebind_subsystems(root, added_mask);
 	if (ret)
 		goto out_unlock;
 
+	rebind_subsystems(&cgroup_dummy_root, removed_mask);
+
 	if (opts.release_agent) {
 		spin_lock(&release_agent_path_lock);
 		strcpy(root->release_agent_path, opts.release_agent);
@@ -1420,7 +1430,7 @@ static int cgroup_setup_root(struct cgroupfs_root *root, unsigned long ss_mask)
 	if (ret)
 		goto destroy_root;
 
-	ret = rebind_subsystems(root, ss_mask, 0);
+	ret = rebind_subsystems(root, ss_mask);
 	if (ret)
 		goto destroy_root;
 
@@ -4026,6 +4036,8 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 
 	BUG_ON(online_css(css));
 
+	cgroup_dummy_root.subsys_mask |= 1 << ss->id;
+
 	mutex_unlock(&cgroup_mutex);
 	mutex_unlock(&cgroup_tree_mutex);
 }
-- 
1.8.5.3

[PATCH 07/11] cgroup: move ->subsys_mask from cgroupfs_root to cgroup

[Tejun Heo]

cgroupfs_root->subsys_mask represents the controllers attached to the
hierarchy.  This patch moves the field to cgroup.  Subsystem
initialization and rebinding updates the top cgroup's subsys_mask.
For !root cgroups, the subsys_mask bits are set from create_css() and
cleared from kill_css(), which effectively means that all cgroups will
have the same subsys_mask as the top cgroup.

While this doesn't make any difference now, this will help
implementation of the default unified hierarchy where !root cgroups
may have subsets of the top_cgroup's subsys_mask.

While at it, __kill_css() is split out of kill_css().  The former
doesn't care about the subsys_mask while the latter becomes noop if
the controller is already killed and clears the matching bit if not
before proceeding to killing the css.  This will be used later by the
default unified hierarchy implementation.

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 include/linux/cgroup.h |  6 ++---
 kernel/cgroup.c        | 61 ++++++++++++++++++++++++++++++++------------------
 2 files changed, 42 insertions(+), 25 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 9f4f253..3752a01 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -173,6 +173,9 @@ struct cgroup {
 	 */
 	u64 serial_nr;
 
+	/* The bitmask of subsystems attached to this cgroup */
+	unsigned long subsys_mask;
+
 	/* Private pointers for each registered subsystem */
 	struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
 
@@ -276,9 +279,6 @@ enum {
 struct cgroupfs_root {
 	struct kernfs_root *kf_root;
 
-	/* The bitmask of subsystems attached to this hierarchy */
-	unsigned long subsys_mask;
-
 	/* Unique id for this hierarchy. */
 	int hierarchy_id;
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 9b9a294..7505f8b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -526,7 +526,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset,
 	 * won't change, so no need for locking.
 	 */
 	for_each_subsys(ss, i) {
-		if (root->subsys_mask & (1UL << i)) {
+		if (root->top_cgroup.subsys_mask & (1UL << i)) {
 			/* Subsystem is in this hierarchy. So we want
 			 * the subsystem state from the new
 			 * cgroup */
@@ -739,7 +739,7 @@ static void cgroup_destroy_root(struct cgroupfs_root *root)
 	BUG_ON(!list_empty(&cgrp->children));
 
 	/* Rebind all subsystems back to the default hierarchy */
-	rebind_subsystems(&cgroup_dummy_root, root->subsys_mask);
+	rebind_subsystems(&cgroup_dummy_root, cgrp->subsys_mask);
 
 	/*
 	 * Release all the links from cset_links to this hierarchy's
@@ -1038,8 +1038,8 @@ static int rebind_subsystems(struct cgroupfs_root *dst_root,
 		ss->root = dst_root;
 		css->cgroup = dst_top;
 
-		src_root->subsys_mask &= ~(1 << ssid);
-		dst_root->subsys_mask |= 1 << ssid;
+		src_top->subsys_mask &= ~(1 << ssid);
+		dst_top->subsys_mask |= 1 << ssid;
 
 		if (ss->bind)
 			ss->bind(css);
@@ -1058,7 +1058,7 @@ static int cgroup_show_options(struct seq_file *seq,
 	int ssid;
 
 	for_each_subsys(ss, ssid)
-		if (root->subsys_mask & (1 << ssid))
+		if (root->top_cgroup.subsys_mask & (1 << ssid))
 			seq_printf(seq, ",%s", ss->name);
 	if (root->flags & CGRP_ROOT_SANE_BEHAVIOR)
 		seq_puts(seq, ",sane_behavior");
@@ -1262,12 +1262,12 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
 	if (ret)
 		goto out_unlock;
 
-	if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
+	if (opts.subsys_mask != root->top_cgroup.subsys_mask || opts.release_agent)
 		pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
 			   task_tgid_nr(current), current->comm);
 
-	added_mask = opts.subsys_mask & ~root->subsys_mask;
-	removed_mask = root->subsys_mask & ~opts.subsys_mask;
+	added_mask = opts.subsys_mask & ~root->top_cgroup.subsys_mask;
+	removed_mask = root->top_cgroup.subsys_mask & ~opts.subsys_mask;
 
 	/* Don't allow flags or name to change at remount */
 	if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) ||
@@ -1515,7 +1515,7 @@ retry:
 		 * subsystems) then they must match.
 		 */
 		if ((opts.subsys_mask || opts.none) &&
-		    (opts.subsys_mask != root->subsys_mask)) {
+		    (opts.subsys_mask != root->top_cgroup.subsys_mask)) {
 			if (!name_match)
 				continue;
 			ret = -EBUSY;
@@ -3594,6 +3594,8 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
 	cgroup_get(cgrp);
 	css_get(css->parent);
 
+	cgrp->subsys_mask |= 1 << ss->id;
+
 	if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
 	    parent->parent) {
 		pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
@@ -3700,7 +3702,7 @@ static long cgroup_create(struct cgroup *parent, const char *name,
 
 	/* let's create and online css's */
 	for_each_subsys(ss, ssid) {
-		if (root->subsys_mask & (1 << ssid)) {
+		if (root->top_cgroup.subsys_mask & (1 << ssid)) {
 			err = create_css(cgrp, ss);
 			if (err)
 				goto err_destroy;
@@ -3788,17 +3790,10 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
 	queue_work(cgroup_destroy_wq, &css->destroy_work);
 }
 
-/**
- * kill_css - destroy a css
- * @css: css to destroy
- *
- * This function initiates destruction of @css by removing cgroup interface
- * files and putting its base reference.  ->css_offline() will be invoked
- * asynchronously once css_tryget() is guaranteed to fail and when the
- * reference count reaches zero, @css will be released.
- */
-static void kill_css(struct cgroup_subsys_state *css)
+static void __kill_css(struct cgroup_subsys_state *css)
 {
+	lockdep_assert_held(&cgroup_tree_mutex);
+
 	/*
 	 * This must happen before css is disassociated with its cgroup.
 	 * See seq_css() for details.
@@ -3825,6 +3820,28 @@ static void kill_css(struct cgroup_subsys_state *css)
 }
 
 /**
+ * kill_css - destroy a css
+ * @css: css to destroy
+ *
+ * This function initiates destruction of @css by removing cgroup interface
+ * files and putting its base reference.  ->css_offline() will be invoked
+ * asynchronously once css_tryget() is guaranteed to fail and when the
+ * reference count reaches zero, @css will be released.
+ */
+static void kill_css(struct cgroup_subsys_state *css)
+{
+	struct cgroup *cgrp = css->cgroup;
+
+	lockdep_assert_held(&cgroup_tree_mutex);
+
+	/* if already killed, noop */
+	if (cgrp->subsys_mask & (1 << css->ss->id)) {
+		cgrp->subsys_mask &= ~(1 << css->ss->id);
+		__kill_css(css);
+	}
+}
+
+/**
  * cgroup_destroy_locked - the first stage of cgroup destruction
  * @cgrp: cgroup to be destroyed
  *
@@ -4036,7 +4053,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 
 	BUG_ON(online_css(css));
 
-	cgroup_dummy_root.subsys_mask |= 1 << ss->id;
+	cgroup_dummy_root.top_cgroup.subsys_mask |= 1 << ss->id;
 
 	mutex_unlock(&cgroup_mutex);
 	mutex_unlock(&cgroup_tree_mutex);
@@ -4192,7 +4209,7 @@ int proc_cgroup_show(struct seq_file *m, void *v)
 
 		seq_printf(m, "%d:", root->hierarchy_id);
 		for_each_subsys(ss, ssid)
-			if (root->subsys_mask & (1 << ssid))
+			if (root->top_cgroup.subsys_mask & (1 << ssid))
 				seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
 		if (strlen(root->name))
 			seq_printf(m, "%sname=%s", count ? "," : "",
-- 
1.8.5.3

[PATCH 08/11] cgroup: rename cgroup_dummy_root and related names

[Tejun Heo]

The dummy root will be repurposed to serve as the default unified
hierarchy.  Let's rename things in preparation.

* s/cgroup_dummy_root/cgrp_dfl_root/
* s/cgroupfs_root/cgroup_root/ as we don't do fs part directly anymore
* s/cgroup_root->top_cgroup/cgroup_root->cgrp/ for brevity

This is pure rename.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 include/linux/cgroup.h |  14 ++---
 kernel/cgroup.c        | 168 ++++++++++++++++++++++++-------------------------
 2 files changed, 88 insertions(+), 94 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 3752a01..77294fc 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -24,7 +24,7 @@
 
 #ifdef CONFIG_CGROUPS
 
-struct cgroupfs_root;
+struct cgroup_root;
 struct cgroup_subsys;
 struct inode;
 struct cgroup;
@@ -179,7 +179,7 @@ struct cgroup {
 	/* Private pointers for each registered subsystem */
 	struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
 
-	struct cgroupfs_root *root;
+	struct cgroup_root *root;
 
 	/*
 	 * List of cgrp_cset_links pointing at css_sets with tasks in this
@@ -211,7 +211,7 @@ struct cgroup {
 
 #define MAX_CGROUP_ROOT_NAMELEN 64
 
-/* cgroupfs_root->flags */
+/* cgroup_root->flags */
 enum {
 	/*
 	 * Unfortunately, cgroup core and various controllers are riddled
@@ -272,18 +272,18 @@ enum {
 };
 
 /*
- * A cgroupfs_root represents the root of a cgroup hierarchy, and may be
+ * A cgroup_root represents the root of a cgroup hierarchy, and may be
  * associated with a kernfs_root to form an active hierarchy.  This is
  * internal to cgroup core.  Don't access directly from controllers.
  */
-struct cgroupfs_root {
+struct cgroup_root {
 	struct kernfs_root *kf_root;
 
 	/* Unique id for this hierarchy. */
 	int hierarchy_id;
 
 	/* The root cgroup.  Root is destroyed on its release. */
-	struct cgroup top_cgroup;
+	struct cgroup cgrp;
 
 	/* Number of cgroups in the hierarchy, used only for /proc/cgroups */
 	atomic_t nr_cgrps;
@@ -598,7 +598,7 @@ struct cgroup_subsys {
 	const char *name;
 
 	/* link to parent, protected by cgroup_lock() */
-	struct cgroupfs_root *root;
+	struct cgroup_root *root;
 
 	/*
 	 * List of cftypes.  Each entry is the first entry of an array
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7505f8b..04f6262 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -138,14 +138,11 @@ static const char *cgroup_subsys_name[] = {
 #undef SUBSYS
 
 /*
- * The dummy hierarchy, reserved for the subsystems that are otherwise
+ * The default hierarchy, reserved for the subsystems that are otherwise
  * unattached - it never has more than a single cgroup, and all tasks are
  * part of that cgroup.
  */
-static struct cgroupfs_root cgroup_dummy_root;
-
-/* dummy_top is a shorthand for the dummy hierarchy's top cgroup */
-static struct cgroup * const cgroup_dummy_top = &cgroup_dummy_root.top_cgroup;
+static struct cgroup_root cgrp_dfl_root;
 
 /* The list of hierarchy roots */
 
@@ -175,7 +172,7 @@ static int need_forkexit_callback __read_mostly;
 static struct cftype cgroup_base_files[];
 
 static void cgroup_put(struct cgroup *cgrp);
-static int rebind_subsystems(struct cgroupfs_root *dst_root,
+static int rebind_subsystems(struct cgroup_root *dst_root,
 			     unsigned long ss_mask);
 static void cgroup_destroy_css_killed(struct cgroup *cgrp);
 static int cgroup_destroy_locked(struct cgroup *cgrp);
@@ -514,7 +511,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset,
 					struct cgroup *cgrp,
 					struct cgroup_subsys_state *template[])
 {
-	struct cgroupfs_root *root = cgrp->root;
+	struct cgroup_root *root = cgrp->root;
 	struct cgroup_subsys *ss;
 	struct css_set *cset;
 	unsigned long key;
@@ -526,7 +523,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset,
 	 * won't change, so no need for locking.
 	 */
 	for_each_subsys(ss, i) {
-		if (root->top_cgroup.subsys_mask & (1UL << i)) {
+		if (root->cgrp.subsys_mask & (1UL << i)) {
 			/* Subsystem is in this hierarchy. So we want
 			 * the subsystem state from the new
 			 * cgroup */
@@ -685,14 +682,14 @@ static struct css_set *find_css_set(struct css_set *old_cset,
 	return cset;
 }
 
-static struct cgroupfs_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
+static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
 {
-	struct cgroup *top_cgrp = kf_root->kn->priv;
+	struct cgroup *root_cgrp = kf_root->kn->priv;
 
-	return top_cgrp->root;
+	return root_cgrp->root;
 }
 
-static int cgroup_init_root_id(struct cgroupfs_root *root)
+static int cgroup_init_root_id(struct cgroup_root *root)
 {
 	int id;
 
@@ -706,7 +703,7 @@ static int cgroup_init_root_id(struct cgroupfs_root *root)
 	return 0;
 }
 
-static void cgroup_exit_root_id(struct cgroupfs_root *root)
+static void cgroup_exit_root_id(struct cgroup_root *root)
 {
 	lockdep_assert_held(&cgroup_mutex);
 
@@ -716,7 +713,7 @@ static void cgroup_exit_root_id(struct cgroupfs_root *root)
 	}
 }
 
-static void cgroup_free_root(struct cgroupfs_root *root)
+static void cgroup_free_root(struct cgroup_root *root)
 {
 	if (root) {
 		/* hierarhcy ID shoulid already have been released */
@@ -727,9 +724,9 @@ static void cgroup_free_root(struct cgroupfs_root *root)
 	}
 }
 
-static void cgroup_destroy_root(struct cgroupfs_root *root)
+static void cgroup_destroy_root(struct cgroup_root *root)
 {
-	struct cgroup *cgrp = &root->top_cgroup;
+	struct cgroup *cgrp = &root->cgrp;
 	struct cgrp_cset_link *link, *tmp_link;
 
 	mutex_lock(&cgroup_tree_mutex);
@@ -739,7 +736,7 @@ static void cgroup_destroy_root(struct cgroupfs_root *root)
 	BUG_ON(!list_empty(&cgrp->children));
 
 	/* Rebind all subsystems back to the default hierarchy */
-	rebind_subsystems(&cgroup_dummy_root, cgrp->subsys_mask);
+	rebind_subsystems(&cgrp_dfl_root, cgrp->subsys_mask);
 
 	/*
 	 * Release all the links from cset_links to this hierarchy's
@@ -770,7 +767,7 @@ static void cgroup_destroy_root(struct cgroupfs_root *root)
 
 /* look up cgroup associated with given css_set on the specified hierarchy */
 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
-					    struct cgroupfs_root *root)
+					    struct cgroup_root *root)
 {
 	struct cgroup *res = NULL;
 
@@ -778,7 +775,7 @@ static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
 	lockdep_assert_held(&css_set_rwsem);
 
 	if (cset == &init_css_set) {
-		res = &root->top_cgroup;
+		res = &root->cgrp;
 	} else {
 		struct cgrp_cset_link *link;
 
@@ -801,7 +798,7 @@ static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
  * called with cgroup_mutex and css_set_rwsem held.
  */
 static struct cgroup *task_cgroup_from_root(struct task_struct *task,
-					    struct cgroupfs_root *root)
+					    struct cgroup_root *root)
 {
 	/*
 	 * No need to lock the task - since we hold cgroup_mutex the
@@ -837,9 +834,9 @@ static struct cgroup *task_cgroup_from_root(struct task_struct *task,
  * A cgroup can only be deleted if both its 'count' of using tasks
  * is zero, and its list of 'children' cgroups is empty.  Since all
  * tasks in the system use _some_ cgroup, and since there is always at
- * least one task in the system (init, pid == 1), therefore, top_cgroup
+ * least one task in the system (init, pid == 1), therefore, root cgroup
  * always has either children cgroups and/or using tasks.  So we don't
- * need a special hack to ensure that top_cgroup cannot be deleted.
+ * need a special hack to ensure that root cgroup cannot be deleted.
  *
  * P.S.  One more locking exception.  RCU is used to guard the
  * update of a tasks cgroup pointer by cgroup_attach_task()
@@ -905,7 +902,7 @@ static void cgroup_free_fn(struct work_struct *work)
 		kfree(cgrp);
 	} else {
 		/*
-		 * This is top cgroup's refcnt reaching zero, which
+		 * This is root cgroup's refcnt reaching zero, which
 		 * indicates that the root should be released.
 		 */
 		cgroup_destroy_root(cgrp->root);
@@ -976,10 +973,9 @@ static void cgroup_clear_dir(struct cgroup *cgrp, unsigned long subsys_mask)
 	}
 }
 
-static int rebind_subsystems(struct cgroupfs_root *dst_root,
+static int rebind_subsystems(struct cgroup_root *dst_root,
 			     unsigned long ss_mask)
 {
-	struct cgroup *dst_top = &dst_root->top_cgroup;
 	struct cgroup_subsys *ss;
 	int ssid, ret;
 
@@ -991,20 +987,20 @@ static int rebind_subsystems(struct cgroupfs_root *dst_root,
 			continue;
 
 		/* if @ss is on the dummy_root, we can always move it */
-		if (ss->root == &cgroup_dummy_root)
+		if (ss->root == &cgrp_dfl_root)
 			continue;
 
 		/* if @ss has non-root cgroups attached to it, can't move */
-		if (!list_empty(&ss->root->top_cgroup.children))
+		if (!list_empty(&ss->root->cgrp.children))
 			return -EBUSY;
 
 		/* can't move between two non-dummy roots either */
-		if (dst_root != &cgroup_dummy_root)
+		if (dst_root != &cgrp_dfl_root)
 			return -EBUSY;
 	}
 
-	if (dst_root != &cgroup_dummy_root) {
-		ret = cgroup_populate_dir(dst_top, ss_mask);
+	if (dst_root != &cgrp_dfl_root) {
+		ret = cgroup_populate_dir(&dst_root->cgrp, ss_mask);
 		if (ret)
 			return ret;
 	}
@@ -1015,50 +1011,48 @@ static int rebind_subsystems(struct cgroupfs_root *dst_root,
 	 */
 	mutex_unlock(&cgroup_mutex);
 	for_each_subsys(ss, ssid)
-		if ((ss_mask & (1 << ssid)) && ss->root != &cgroup_dummy_root)
-			cgroup_clear_dir(&ss->root->top_cgroup, 1 << ssid);
+		if ((ss_mask & (1 << ssid)) && ss->root != &cgrp_dfl_root)
+			cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);
 	mutex_lock(&cgroup_mutex);
 
 	for_each_subsys(ss, ssid) {
-		struct cgroupfs_root *src_root;
-		struct cgroup *src_top;
+		struct cgroup_root *src_root;
 		struct cgroup_subsys_state *css;
 
 		if (!(ss_mask & (1 << ssid)))
 			continue;
 
 		src_root = ss->root;
-		src_top = &src_root->top_cgroup;
-		css = cgroup_css(src_top, ss);
+		css = cgroup_css(&src_root->cgrp, ss);
 
-		WARN_ON(!css || cgroup_css(dst_top, ss));
+		WARN_ON(!css || cgroup_css(&dst_root->cgrp, ss));
 
-		RCU_INIT_POINTER(src_top->subsys[ssid], NULL);
-		rcu_assign_pointer(dst_top->subsys[ssid], css);
+		RCU_INIT_POINTER(src_root->cgrp.subsys[ssid], NULL);
+		rcu_assign_pointer(dst_root->cgrp.subsys[ssid], css);
 		ss->root = dst_root;
-		css->cgroup = dst_top;
+		css->cgroup = &dst_root->cgrp;
 
-		src_top->subsys_mask &= ~(1 << ssid);
-		dst_top->subsys_mask |= 1 << ssid;
+		src_root->cgrp.subsys_mask &= ~(1 << ssid);
+		dst_root->cgrp.subsys_mask |= 1 << ssid;
 
 		if (ss->bind)
 			ss->bind(css);
 	}
 
-	if (dst_root != &cgroup_dummy_root)
-		kernfs_activate(dst_top->kn);
+	if (dst_root != &cgrp_dfl_root)
+		kernfs_activate(dst_root->cgrp.kn);
 	return 0;
 }
 
 static int cgroup_show_options(struct seq_file *seq,
 			       struct kernfs_root *kf_root)
 {
-	struct cgroupfs_root *root = cgroup_root_from_kf(kf_root);
+	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
 	struct cgroup_subsys *ss;
 	int ssid;
 
 	for_each_subsys(ss, ssid)
-		if (root->top_cgroup.subsys_mask & (1 << ssid))
+		if (root->cgrp.subsys_mask & (1 << ssid))
 			seq_printf(seq, ",%s", ss->name);
 	if (root->flags & CGRP_ROOT_SANE_BEHAVIOR)
 		seq_puts(seq, ",sane_behavior");
@@ -1072,7 +1066,7 @@ static int cgroup_show_options(struct seq_file *seq,
 		seq_printf(seq, ",release_agent=%s", root->release_agent_path);
 	spin_unlock(&release_agent_path_lock);
 
-	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags))
+	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
 		seq_puts(seq, ",clone_children");
 	if (strlen(root->name))
 		seq_printf(seq, ",name=%s", root->name);
@@ -1245,7 +1239,7 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
 static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
 {
 	int ret = 0;
-	struct cgroupfs_root *root = cgroup_root_from_kf(kf_root);
+	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
 	struct cgroup_sb_opts opts;
 	unsigned long added_mask, removed_mask;
 
@@ -1262,12 +1256,12 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
 	if (ret)
 		goto out_unlock;
 
-	if (opts.subsys_mask != root->top_cgroup.subsys_mask || opts.release_agent)
+	if (opts.subsys_mask != root->cgrp.subsys_mask || opts.release_agent)
 		pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
 			   task_tgid_nr(current), current->comm);
 
-	added_mask = opts.subsys_mask & ~root->top_cgroup.subsys_mask;
-	removed_mask = root->top_cgroup.subsys_mask & ~opts.subsys_mask;
+	added_mask = opts.subsys_mask & ~root->cgrp.subsys_mask;
+	removed_mask = root->cgrp.subsys_mask & ~opts.subsys_mask;
 
 	/* Don't allow flags or name to change at remount */
 	if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) ||
@@ -1280,7 +1274,7 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
 	}
 
 	/* remounting is not allowed for populated hierarchies */
-	if (!list_empty(&root->top_cgroup.children)) {
+	if (!list_empty(&root->cgrp.children)) {
 		ret = -EBUSY;
 		goto out_unlock;
 	}
@@ -1289,7 +1283,7 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
 	if (ret)
 		goto out_unlock;
 
-	rebind_subsystems(&cgroup_dummy_root, removed_mask);
+	rebind_subsystems(&cgrp_dfl_root, removed_mask);
 
 	if (opts.release_agent) {
 		spin_lock(&release_agent_path_lock);
@@ -1368,10 +1362,10 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
 	cgrp->dummy_css.cgroup = cgrp;
 }
 
-static void init_cgroup_root(struct cgroupfs_root *root,
+static void init_cgroup_root(struct cgroup_root *root,
 			     struct cgroup_sb_opts *opts)
 {
-	struct cgroup *cgrp = &root->top_cgroup;
+	struct cgroup *cgrp = &root->cgrp;
 
 	INIT_LIST_HEAD(&root->root_list);
 	atomic_set(&root->nr_cgrps, 1);
@@ -1385,13 +1379,13 @@ static void init_cgroup_root(struct cgroupfs_root *root,
 	if (opts->name)
 		strcpy(root->name, opts->name);
 	if (opts->cpuset_clone_children)
-		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags);
+		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
 }
 
-static int cgroup_setup_root(struct cgroupfs_root *root, unsigned long ss_mask)
+static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
 {
 	LIST_HEAD(tmp_links);
-	struct cgroup *root_cgrp = &root->top_cgroup;
+	struct cgroup *root_cgrp = &root->cgrp;
 	struct css_set *cset;
 	int i, ret;
 
@@ -1443,7 +1437,7 @@ static int cgroup_setup_root(struct cgroupfs_root *root, unsigned long ss_mask)
 	cgroup_root_count++;
 
 	/*
-	 * Link the top cgroup in this hierarchy into all the css_set
+	 * Link the root cgroup in this hierarchy into all the css_set
 	 * objects.
 	 */
 	down_write(&css_set_rwsem);
@@ -1472,7 +1466,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
 			 int flags, const char *unused_dev_name,
 			 void *data)
 {
-	struct cgroupfs_root *root;
+	struct cgroup_root *root;
 	struct cgroup_sb_opts opts;
 	struct dentry *dentry;
 	int ret;
@@ -1496,7 +1490,7 @@ retry:
 	for_each_root(root) {
 		bool name_match = false;
 
-		if (root == &cgroup_dummy_root)
+		if (root == &cgrp_dfl_root)
 			continue;
 
 		/*
@@ -1515,7 +1509,7 @@ retry:
 		 * subsystems) then they must match.
 		 */
 		if ((opts.subsys_mask || opts.none) &&
-		    (opts.subsys_mask != root->top_cgroup.subsys_mask)) {
+		    (opts.subsys_mask != root->cgrp.subsys_mask)) {
 			if (!name_match)
 				continue;
 			ret = -EBUSY;
@@ -1533,13 +1527,13 @@ retry:
 		}
 
 		/*
-		 * A root's lifetime is governed by its top cgroup.  Zero
+		 * A root's lifetime is governed by its root cgroup.  Zero
 		 * ref indicate that the root is being destroyed.  Wait for
 		 * destruction to complete so that the subsystems are free.
 		 * We can use wait_queue for the wait but this path is
 		 * super cold.  Let's just sleep for a bit and retry.
 		 */
-		if (!atomic_inc_not_zero(&root->top_cgroup.refcnt)) {
+		if (!atomic_inc_not_zero(&root->cgrp.refcnt)) {
 			mutex_unlock(&cgroup_mutex);
 			mutex_unlock(&cgroup_tree_mutex);
 			kfree(opts.release_agent);
@@ -1586,16 +1580,16 @@ out_unlock:
 
 	dentry = kernfs_mount(fs_type, flags, root->kf_root);
 	if (IS_ERR(dentry))
-		cgroup_put(&root->top_cgroup);
+		cgroup_put(&root->cgrp);
 	return dentry;
 }
 
 static void cgroup_kill_sb(struct super_block *sb)
 {
 	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
-	struct cgroupfs_root *root = cgroup_root_from_kf(kf_root);
+	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
 
-	cgroup_put(&root->top_cgroup);
+	cgroup_put(&root->cgrp);
 	kernfs_kill_sb(sb);
 }
 
@@ -1622,7 +1616,7 @@ static struct kobject *cgroup_kobj;
  */
 char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 {
-	struct cgroupfs_root *root;
+	struct cgroup_root *root;
 	struct cgroup *cgrp;
 	int hierarchy_id = 1;
 	char *path = NULL;
@@ -2112,14 +2106,14 @@ out_unlock_cgroup:
  */
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 {
-	struct cgroupfs_root *root;
+	struct cgroup_root *root;
 	int retval = 0;
 
 	mutex_lock(&cgroup_mutex);
 	for_each_root(root) {
 		struct cgroup *from_cgrp;
 
-		if (root == &cgroup_dummy_root)
+		if (root == &cgrp_dfl_root)
 			continue;
 
 		down_read(&css_set_rwsem);
@@ -2151,7 +2145,7 @@ static int cgroup_procs_write(struct cgroup_subsys_state *css,
 static int cgroup_release_agent_write(struct cgroup_subsys_state *css,
 				      struct cftype *cft, const char *buffer)
 {
-	struct cgroupfs_root *root = css->cgroup->root;
+	struct cgroup_root *root = css->cgroup->root;
 
 	BUILD_BUG_ON(sizeof(root->release_agent_path) < PATH_MAX);
 	if (!cgroup_lock_live_group(css->cgroup))
@@ -2362,14 +2356,14 @@ static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
 {
 	LIST_HEAD(pending);
 	struct cgroup_subsys *ss = cfts[0].ss;
-	struct cgroup *root = &ss->root->top_cgroup;
+	struct cgroup *root = &ss->root->cgrp;
 	struct cgroup_subsys_state *css;
 	int ret = 0;
 
 	lockdep_assert_held(&cgroup_tree_mutex);
 
 	/* don't bother if @ss isn't attached */
-	if (ss->root == &cgroup_dummy_root)
+	if (ss->root == &cgrp_dfl_root)
 		return 0;
 
 	/* add/rm files for all cgroups created before */
@@ -3623,7 +3617,7 @@ static long cgroup_create(struct cgroup *parent, const char *name,
 			  umode_t mode)
 {
 	struct cgroup *cgrp;
-	struct cgroupfs_root *root = parent->root;
+	struct cgroup_root *root = parent->root;
 	int ssid, err;
 	struct cgroup_subsys *ss;
 	struct kernfs_node *kn;
@@ -3702,7 +3696,7 @@ static long cgroup_create(struct cgroup *parent, const char *name,
 
 	/* let's create and online css's */
 	for_each_subsys(ss, ssid) {
-		if (root->top_cgroup.subsys_mask & (1 << ssid)) {
+		if (root->cgrp.subsys_mask & (1 << ssid)) {
 			err = create_css(cgrp, ss);
 			if (err)
 				goto err_destroy;
@@ -4031,17 +4025,17 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 
 	INIT_LIST_HEAD(&ss->cfts);
 
-	/* Create the top cgroup state for this subsystem */
-	ss->root = &cgroup_dummy_root;
-	css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss));
+	/* Create the root cgroup state for this subsystem */
+	ss->root = &cgrp_dfl_root;
+	css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
 	/* We don't handle early failures gracefully */
 	BUG_ON(IS_ERR(css));
-	init_css(css, ss, cgroup_dummy_top);
+	init_css(css, ss, &cgrp_dfl_root.cgrp);
 
 	/* Update the init_css_set to contain a subsys
 	 * pointer to this state - since the subsystem is
 	 * newly registered, all tasks and hence the
-	 * init_css_set is in the subsystem's top cgroup. */
+	 * init_css_set is in the subsystem's root cgroup. */
 	init_css_set.subsys[ss->id] = css;
 
 	need_forkexit_callback |= ss->fork || ss->exit;
@@ -4053,7 +4047,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 
 	BUG_ON(online_css(css));
 
-	cgroup_dummy_root.top_cgroup.subsys_mask |= 1 << ss->id;
+	cgrp_dfl_root.cgrp.subsys_mask |= 1 << ss->id;
 
 	mutex_unlock(&cgroup_mutex);
 	mutex_unlock(&cgroup_tree_mutex);
@@ -4071,7 +4065,7 @@ int __init cgroup_init_early(void)
 	struct cgroup_subsys *ss;
 	int i;
 
-	init_cgroup_root(&cgroup_dummy_root, &opts);
+	init_cgroup_root(&cgrp_dfl_root, &opts);
 	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
 
 	for_each_subsys(ss, i) {
@@ -4112,7 +4106,7 @@ int __init cgroup_init(void)
 	key = css_set_hash(init_css_set.subsys);
 	hash_add(css_set_table, &init_css_set.hlist, key);
 
-	BUG_ON(cgroup_setup_root(&cgroup_dummy_root, 0));
+	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
 
 	mutex_unlock(&cgroup_mutex);
 	mutex_unlock(&cgroup_tree_mutex);
@@ -4181,7 +4175,7 @@ int proc_cgroup_show(struct seq_file *m, void *v)
 	struct task_struct *tsk;
 	char *buf, *path;
 	int retval;
-	struct cgroupfs_root *root;
+	struct cgroup_root *root;
 
 	retval = -ENOMEM;
 	buf = kmalloc(PATH_MAX, GFP_KERNEL);
@@ -4204,12 +4198,12 @@ int proc_cgroup_show(struct seq_file *m, void *v)
 		struct cgroup *cgrp;
 		int ssid, count = 0;
 
-		if (root == &cgroup_dummy_root)
+		if (root == &cgrp_dfl_root)
 			continue;
 
 		seq_printf(m, "%d:", root->hierarchy_id);
 		for_each_subsys(ss, ssid)
-			if (root->top_cgroup.subsys_mask & (1 << ssid))
+			if (root->cgrp.subsys_mask & (1 << ssid))
 				seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
 		if (strlen(root->name))
 			seq_printf(m, "%sname=%s", count ? "," : "",
@@ -4639,7 +4633,7 @@ static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
 		struct cgroup *c = link->cgrp;
 		const char *name = "?";
 
-		if (c != cgroup_dummy_top) {
+		if (c != &cgrp_dfl_root.cgrp) {
 			cgroup_name(c, name_buf, NAME_MAX + 1);
 			name = name_buf;
 		}
-- 
1.8.5.3

[PATCH 09/11] cgroup: drop const from @buffer of cftype->write_string()

[Tejun Heo]

cftype->write_string() just passes on the writeable buffer from kernfs
and there's no reason to add const restriction on the buffer.  The
only thing const achieves is unnecessarily complicating parsing of the
buffer.  Drop const from @buffer.

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Cc: Peter Zijlstra <a.p.zijlstra-/NLkJaSkS4VmR6Xm/wNWPw@public.gmane.org>
Cc: Paul Mackerras <paulus-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>
Cc: Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Arnaldo Carvalho de Melo <acme-f8uhVLnGfZaxAyOMLChx1axOck334EZe@public.gmane.org>
Cc: Daniel Borkmann <dborkman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
Cc: Balbir Singh <bsingharora-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
---
 block/blk-throttle.c      | 4 ++--
 block/cfq-iosched.c       | 4 ++--
 include/linux/cgroup.h    | 2 +-
 kernel/cgroup.c           | 2 +-
 kernel/cgroup_freezer.c   | 2 +-
 kernel/cpuset.c           | 2 +-
 mm/hugetlb_cgroup.c       | 2 +-
 mm/memcontrol.c           | 4 ++--
 net/core/netprio_cgroup.c | 2 +-
 net/ipv4/tcp_memcontrol.c | 2 +-
 security/device_cgroup.c  | 4 ++--
 11 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 861c363..033745c 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1408,13 +1408,13 @@ static int tg_set_conf(struct cgroup_subsys_state *css, struct cftype *cft,
 }
 
 static int tg_set_conf_u64(struct cgroup_subsys_state *css, struct cftype *cft,
-			   const char *buf)
+			   char *buf)
 {
 	return tg_set_conf(css, cft, buf, true);
 }
 
 static int tg_set_conf_uint(struct cgroup_subsys_state *css, struct cftype *cft,
-			    const char *buf)
+			    char *buf)
 {
 	return tg_set_conf(css, cft, buf, false);
 }
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 4611879..f5de45b 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1701,13 +1701,13 @@ static int __cfqg_set_weight_device(struct cgroup_subsys_state *css,
 }
 
 static int cfqg_set_weight_device(struct cgroup_subsys_state *css,
-				  struct cftype *cft, const char *buf)
+				  struct cftype *cft, char *buf)
 {
 	return __cfqg_set_weight_device(css, cft, buf, false);
 }
 
 static int cfqg_set_leaf_weight_device(struct cgroup_subsys_state *css,
-				       struct cftype *cft, const char *buf)
+				       struct cftype *cft, char *buf)
 {
 	return __cfqg_set_weight_device(css, cft, buf, true);
 }
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 77294fc..79993ac 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -454,7 +454,7 @@ struct cftype {
 	 * Returns 0 or -ve error code.
 	 */
 	int (*write_string)(struct cgroup_subsys_state *css, struct cftype *cft,
-			    const char *buffer);
+			    char *buffer);
 	/*
 	 * trigger() callback can be used to get some kick from the
 	 * userspace, when the actual string written is not important
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 04f6262..36d1a53 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2143,7 +2143,7 @@ static int cgroup_procs_write(struct cgroup_subsys_state *css,
 }
 
 static int cgroup_release_agent_write(struct cgroup_subsys_state *css,
-				      struct cftype *cft, const char *buffer)
+				      struct cftype *cft, char *buffer)
 {
 	struct cgroup_root *root = css->cgroup->root;
 
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 2ea98b2..2bc4a22 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -442,7 +442,7 @@ static void freezer_change_state(struct freezer *freezer, bool freeze)
 }
 
 static int freezer_write(struct cgroup_subsys_state *css, struct cftype *cft,
-			 const char *buffer)
+			 char *buffer)
 {
 	bool freeze;
 
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 8d53245..efbf9ba 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1610,7 +1610,7 @@ out_unlock:
  * Common handling for a write to a "cpus" or "mems" file.
  */
 static int cpuset_write_resmask(struct cgroup_subsys_state *css,
-				struct cftype *cft, const char *buf)
+				struct cftype *cft, char *buf)
 {
 	struct cpuset *cs = css_cs(css);
 	struct cpuset *trialcs;
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index b135853..595d7fd 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -254,7 +254,7 @@ static u64 hugetlb_cgroup_read_u64(struct cgroup_subsys_state *css,
 }
 
 static int hugetlb_cgroup_write(struct cgroup_subsys_state *css,
-				struct cftype *cft, const char *buffer)
+				struct cftype *cft, char *buffer)
 {
 	int idx, name, ret;
 	unsigned long long val;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d9c6ac1..96f94a9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5242,7 +5242,7 @@ static int memcg_update_kmem_limit(struct mem_cgroup *memcg,
  * RES_LIMIT.
  */
 static int mem_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
-			    const char *buffer)
+			    char *buffer)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 	enum res_type type;
@@ -6063,7 +6063,7 @@ static void memcg_event_ptable_queue_proc(struct file *file,
  * Interpretation of args is defined by control file implementation.
  */
 static int memcg_write_event_control(struct cgroup_subsys_state *css,
-				     struct cftype *cft, const char *buffer)
+				     struct cftype *cft, char *buffer)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 	struct mem_cgroup_event *event;
diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index f9f3a40..3825f66 100644
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c
@@ -186,7 +186,7 @@ static int read_priomap(struct seq_file *sf, void *v)
 }
 
 static int write_priomap(struct cgroup_subsys_state *css, struct cftype *cft,
-			 const char *buffer)
+			 char *buffer)
 {
 	char devname[IFNAMSIZ + 1];
 	struct net_device *dev;
diff --git a/net/ipv4/tcp_memcontrol.c b/net/ipv4/tcp_memcontrol.c
index 20a0aca..d4f015a 100644
--- a/net/ipv4/tcp_memcontrol.c
+++ b/net/ipv4/tcp_memcontrol.c
@@ -103,7 +103,7 @@ static int tcp_update_limit(struct mem_cgroup *memcg, u64 val)
 }
 
 static int tcp_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
-			    const char *buffer)
+			    char *buffer)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 	unsigned long long val;
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 7f88bcd..8365909 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -496,7 +496,7 @@ static inline bool has_children(struct dev_cgroup *devcgroup)
  * parent cgroup has the access you're asking for.
  */
 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
-				   int filetype, const char *buffer)
+				   int filetype, char *buffer)
 {
 	const char *b;
 	char temp[12];		/* 11 + 1 characters needed for a u32 */
@@ -652,7 +652,7 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 }
 
 static int devcgroup_access_write(struct cgroup_subsys_state *css,
-				  struct cftype *cft, const char *buffer)
+				  struct cftype *cft, char *buffer)
 {
 	int retval;
 
-- 
1.8.5.3

[PATCH 10/11] cgroup: make cgrp_dfl_root mountable

[Tejun Heo]

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: Tejun Heo <tj@kernel.org>
---
 include/linux/cgroup.h | 10 ++++++
 kernel/cgroup.c        | 94 ++++++++++++++++++++++++++++++++------------------
 2 files changed, 71 insertions(+), 33 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 79993ac..7e9fa50 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -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.
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 36d1a53..c42230c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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)
+	ret = cgroup_populate_dir(&dst_root->cgrp, ss_mask);
+	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);
 
@@ -1039,8 +1057,7 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
 			ss->bind(css);
 	}
 
-	if (dst_root != &cgrp_dfl_root)
-		kernfs_activate(dst_root->cgrp.kn);
+	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;
-		}
 
+		cgroup_name(c, name_buf, NAME_MAX + 1);
 		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);
-- 
1.8.5.3

[PATCH 11/11] cgroup: implement CFTYPE_ONLY_ON_DFL

[Tejun Heo]

This cftype flag makes the file only appear on the default hierarchy.
This will later be used for cgroup.controllers file.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 include/linux/cgroup.h | 1 +
 kernel/cgroup.c        | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 7e9fa50..43d1ed3 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -384,6 +384,7 @@ enum {
 	CFTYPE_NOT_ON_ROOT	= (1 << 1),	/* don't create on root cgrp */
 	CFTYPE_INSANE		= (1 << 2),	/* don't create if sane_behavior */
 	CFTYPE_NO_PREFIX	= (1 << 3),	/* (DON'T USE FOR NEW FILES) no subsys prefix */
+	CFTYPE_ONLY_ON_DFL	= (1 << 4),	/* only on default hierarchy */
 };
 
 #define MAX_CFTYPE_NAME		64
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c42230c..79e3573 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2356,6 +2356,8 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
 
 	for (cft = cfts; cft->name[0] != '\0'; cft++) {
 		/* does cft->flags tell us to skip this file on @cgrp? */
+		if ((cft->flags & CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
+			continue;
 		if ((cft->flags & CFTYPE_INSANE) && cgroup_sane_behavior(cgrp))
 			continue;
 		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
-- 
1.8.5.3

Re: [PATCHSET cgroup/for-3.15] cgroup: prepare for the default unified hierarchy

[Li Zefan]

On 2014/3/14 3:50, Tejun Heo wrote:
> Hello,
> 
> The planned unified hierarchy is just around the corner.  We're gonna
> repurpose the dummy hierarchy to serve as the default unified
> hierarchy.  Controllers which aren't attached to other hierarchies are
> already automatically bound to the dummy hierarchy; however, the dummy
> hierarchy is minimally initialized during boot and can't currently act
> as a full hierarchy.
> 
> This patchset gradually turns the dummy hierarchy into fully
> functional default one and makes it mountable via selecting
> sane_behavior without any subsystems specified.  While this patchset
> does make the default hierarchy mountable, the unified hierarchy
> functionality isn't implemented yet and cgroup creation in the default
> hierarchy is rejected for now.
> 
> This lays down all the boilerplate work for the unified hierarchy.
> The next patchset will implement the actual unified functionality.
> 
> This patchset contains the following eleven patches.
> 
>  0001-cgroup-cgroup-subsys-should-be-cleared-after-the-css.patch
>  0002-cgroup-relocate-setting-of-CGRP_DEAD.patch
>  0003-cgroup-reorganize-cgroup-bootstrapping.patch
>  0004-cgroup-use-cgroup_setup_root-to-initialize-cgroup_du.patch
>  0005-cgroup-remove-NULL-checks-from-pr_cont_-cgroup_-name.patch
>  0006-cgroup-treat-cgroup_dummy_root-as-an-equivalent-hier.patch
>  0007-cgroup-move-subsys_mask-from-cgroupfs_root-to-cgroup.patch
>  0008-cgroup-rename-cgroup_dummy_root-and-related-names.patch
>  0009-cgroup-drop-const-from-buffer-of-cftype-write_string.patch
>  0010-cgroup-make-cgrp_dfl_root-mountable.patch
>  0011-cgroup-implement-CFTYPE_ONLY_ON_DFL.patch
> 
> 0001-0002 are misc fix / prep.
> 
> 0003-0009 (mostly) turn the dummy hierarchy into a full hierarchy
> which takes on controllers which aren't attached to other hierarchies.
> 
> 0010-0011 make the default hierarchy mountable and implement
> CFTYPE_ONLY_DFL.
> 
> This patchset is on top of cgroup/for-3.15 b8dadcb58d54 ("cpuset: use
> rcu_read_lock() to protect task_cs()").  diffstat follows.
> 
>  block/blk-throttle.c      |    4
>  block/cfq-iosched.c       |    4
>  include/linux/cgroup.h    |   57 ++---
>  kernel/cgroup.c           |  464 +++++++++++++++++++++++++---------------------
>  kernel/cgroup_freezer.c   |    2
>  kernel/cpuset.c           |    2
>  mm/hugetlb_cgroup.c       |    2
>  mm/memcontrol.c           |    4
>  net/core/netprio_cgroup.c |    2
>  net/ipv4/tcp_memcontrol.c |    2
>  security/device_cgroup.c  |    4
>  11 files changed, 295 insertions(+), 252 deletions(-)
> 

Looks good in general!

Acked-by: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>

Re: [PATCHSET cgroup/for-3.15] cgroup: prepare for the default unified hierarchy

[Tejun Heo]

On Thu, Mar 13, 2014 at 03:50:02PM -0400, Tejun Heo wrote:
> The planned unified hierarchy is just around the corner.  We're gonna
> repurpose the dummy hierarchy to serve as the default unified
> hierarchy.  Controllers which aren't attached to other hierarchies are
> already automatically bound to the dummy hierarchy; however, the dummy
> hierarchy is minimally initialized during boot and can't currently act
> as a full hierarchy.
> 
> This patchset gradually turns the dummy hierarchy into fully
> functional default one and makes it mountable via selecting
> sane_behavior without any subsystems specified.  While this patchset
> does make the default hierarchy mountable, the unified hierarchy
> functionality isn't implemented yet and cgroup creation in the default
> hierarchy is rejected for now.
> 
> This lays down all the boilerplate work for the unified hierarchy.
> The next patchset will implement the actual unified functionality.
> 
> This patchset contains the following eleven patches.
> 
>  0001-cgroup-cgroup-subsys-should-be-cleared-after-the-css.patch
>  0002-cgroup-relocate-setting-of-CGRP_DEAD.patch
>  0003-cgroup-reorganize-cgroup-bootstrapping.patch
>  0004-cgroup-use-cgroup_setup_root-to-initialize-cgroup_du.patch
>  0005-cgroup-remove-NULL-checks-from-pr_cont_-cgroup_-name.patch
>  0006-cgroup-treat-cgroup_dummy_root-as-an-equivalent-hier.patch
>  0007-cgroup-move-subsys_mask-from-cgroupfs_root-to-cgroup.patch
>  0008-cgroup-rename-cgroup_dummy_root-and-related-names.patch
>  0009-cgroup-drop-const-from-buffer-of-cftype-write_string.patch
>  0010-cgroup-make-cgrp_dfl_root-mountable.patch
>  0011-cgroup-implement-CFTYPE_ONLY_ON_DFL.patch

Applied 0002-0011 to libata/for-3.15.  0001 has the possibility to
make css iterators malfunction as they don't exect the csses to be
NULL.  It will be applied after iterators are updated to handle NULL
csses.

Thanks.

-- 
tejun