[PATCH 06/14] cgroup: move cgroup->sibling and ->children into cgroup_subsys_state

Tejun Heo
2014-05-09T21:34:49Z

We're moving towards using cgroup_subsys_states as the fundamental
structural blocks. Let's move cgroup->sibling and ->children into
cgroup_subsys_state. This is pure move without functional change and
only cgroup->self's fields are actually used. Other csses will make
use of the fields later.

While at it, update init_and_link_css() so that it zeroes the whole
css before initializing it and remove explicit zeroing of ->flags.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/cgroup.h | 11 ++++-------
kernel/cgroup.c | 38 ++++++++++++++++++++------------------
2 files changed, 24 insertions(+), 25 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 5fda088..db8d8c2 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -68,6 +68,10 @@ struct cgroup_subsys_state {
/* PI: the parent css */
struct cgroup_subsys_state *parent;

+ /* siblings list anchored at the parent's ->children */
+ struct list_head sibling;
+ struct list_head children;
+
/*
* PI: Subsys-unique ID. 0 is unused and root is always 1. The
* matching css can be looked up using css_from_id().
@@ -166,13 +170,6 @@ struct cgroup {
*/
int populated_cnt;

- /*
- * We link our 'sibling' struct into our parent's 'children'.
- * Our children link their 'sibling' into our 'children'.
- */
- struct list_head sibling; /* my parent's children */
- struct list_head children; /* my children */
-
struct kernfs_node *kn; /* cgroup kernfs entry */
struct kernfs_node *populated_kn; /* kn for "cgroup.subtree_populated" */

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d61c716..3d6c0aa 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -378,7 +378,7 @@ static int notify_on_release(const struct cgroup *cgrp)

/* iterate over child cgrps, lock should be held throughout iteration */
#define cgroup_for_each_live_child(child, cgrp) \
- list_for_each_entry((child), &(cgrp)->children, sibling) \
+ list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
if (({ lockdep_assert_held(&cgroup_mutex); \
cgroup_is_dead(child); })) \
; \
@@ -870,7 +870,7 @@ static void cgroup_destroy_root(struct cgroup_root *root)
mutex_lock(&cgroup_mutex);

BUG_ON(atomic_read(&root->nr_cgrps));
- BUG_ON(!list_empty(&cgrp->children));
+ BUG_ON(!list_empty(&cgrp->self.children));

/* Rebind all subsystems back to the default hierarchy */
rebind_subsystems(&cgrp_dfl_root, root->subsys_mask);
@@ -1432,7 +1432,7 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
}

/* remounting is not allowed for populated hierarchies */
- if (!list_empty(&root->cgrp.children)) {
+ if (!list_empty(&root->cgrp.self.children)) {
ret = -EBUSY;
goto out_unlock;
}
@@ -1512,8 +1512,8 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
struct cgroup_subsys *ss;
int ssid;

- INIT_LIST_HEAD(&cgrp->sibling);
- INIT_LIST_HEAD(&cgrp->children);
+ INIT_LIST_HEAD(&cgrp->self.sibling);
+ INIT_LIST_HEAD(&cgrp->self.children);
INIT_LIST_HEAD(&cgrp->cset_links);
INIT_LIST_HEAD(&cgrp->release_list);
INIT_LIST_HEAD(&cgrp->pidlists);
@@ -1612,7 +1612,7 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned int ss_mask)
link_css_set(&tmp_links, cset, root_cgrp);
up_write(&css_set_rwsem);

- BUG_ON(!list_empty(&root_cgrp->children));
+ BUG_ON(!list_empty(&root_cgrp->self.children));
BUG_ON(atomic_read(&root->nr_cgrps) != 1);

kernfs_activate(root_cgrp->kn);
@@ -3127,11 +3127,11 @@ css_next_child(struct cgroup_subsys_state *pos_css,
* cgroup is removed or iteration and removal race.
*/
if (!pos) {
- next = list_entry_rcu(cgrp->children.next, struct cgroup, sibling);
+ next = list_entry_rcu(cgrp->self.children.next, struct cgroup, self.sibling);
} else if (likely(!cgroup_is_dead(pos))) {
- next = list_entry_rcu(pos->sibling.next, struct cgroup, sibling);
+ next = list_entry_rcu(pos->self.sibling.next, struct cgroup, self.sibling);
} else {
- list_for_each_entry_rcu(next, &cgrp->children, sibling)
+ list_for_each_entry_rcu(next, &cgrp->self.children, self.sibling)
if (next->serial_nr > pos->serial_nr)
break;
}
@@ -3141,12 +3141,12 @@ css_next_child(struct cgroup_subsys_state *pos_css,
* the next sibling; however, it might have @ss disabled. If so,
* fast-forward to the next enabled one.
*/
- while (&next->sibling != &cgrp->children) {
+ while (&next->self.sibling != &cgrp->self.children) {
struct cgroup_subsys_state *next_css = cgroup_css(next, parent_css->ss);

if (next_css)
return next_css;
- next = list_entry_rcu(next->sibling.next, struct cgroup, sibling);
+ next = list_entry_rcu(next->self.sibling.next, struct cgroup, self.sibling);
}
return NULL;
}
@@ -3282,7 +3282,7 @@ static bool cgroup_has_live_children(struct cgroup *cgrp)
struct cgroup *child;

rcu_read_lock();
- list_for_each_entry_rcu(child, &cgrp->children, sibling) {
+ list_for_each_entry_rcu(child, &cgrp->self.children, self.sibling) {
if (!cgroup_is_dead(child)) {
rcu_read_unlock();
return true;
@@ -4143,7 +4143,7 @@ static void css_release_work_fn(struct work_struct *work)
} else {
/* cgroup release path */
mutex_lock(&cgroup_mutex);
- list_del_rcu(&cgrp->sibling);
+ list_del_rcu(&cgrp->self.sibling);
mutex_unlock(&cgroup_mutex);

cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
@@ -4167,9 +4167,11 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
{
cgroup_get(cgrp);

+ memset(css, 0, sizeof(*css));
css->cgroup = cgrp;
css->ss = ss;
- css->flags = 0;
+ INIT_LIST_HEAD(&css->sibling);
+ INIT_LIST_HEAD(&css->children);

if (cgroup_parent(cgrp)) {
css->parent = cgroup_css(cgroup_parent(cgrp), ss);
@@ -4343,7 +4345,7 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
cgrp->serial_nr = cgroup_serial_nr_next++;

/* allocation complete, commit to creation */
- list_add_tail_rcu(&cgrp->sibling, &cgroup_parent(cgrp)->children);
+ list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
atomic_inc(&root->nr_cgrps);
cgroup_get(parent);

@@ -4506,9 +4508,9 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
return -EBUSY;

/*
- * Make sure there's no live children. We can't test ->children
- * emptiness as dead children linger on it while being destroyed;
- * otherwise, "rmdir parent/child parent" may fail with -EBUSY.
+ * Make sure there's no live children. We can't test emptiness of
+ * ->self.children as dead children linger on it while being
+ * drained; otherwise, "rmdir parent/child parent" may fail.
*/
if (cgroup_has_live_children(cgrp))
return -EBUSY;
--
1.9.0