[PATCH 05/14] cgroup: remove cgroup->parent

Tejun Heo
2014-05-09T21:35:16Z

cgroup->parent is redundant as cgroup->self.parent can also be used to
determine the parent cgroup and we're moving towards using
cgroup_subsys_states as the fundamental structural blocks. This patch
introduces cgroup_parent() which follows cgroup->self.parent and
removes cgroup->parent.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/cgroup.h | 1 -
kernel/cgroup.c | 52 +++++++++++++++++++++++++++++---------------------
2 files changed, 30 insertions(+), 23 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 88c4d03..5fda088 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -173,7 +173,6 @@ struct cgroup {
struct list_head sibling; /* my parent's children */
struct list_head children; /* my children */

- struct cgroup *parent; /* my parent */
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 dab8f35..d61c716 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -218,6 +218,15 @@ static void cgroup_idr_remove(struct idr *idr, int id)
spin_unlock_bh(&cgroup_idr_lock);
}

+static struct cgroup *cgroup_parent(struct cgroup *cgrp)
+{
+ struct cgroup_subsys_state *parent_css = cgrp->self.parent;
+
+ if (parent_css)
+ return container_of(parent_css, struct cgroup, self);
+ return NULL;
+}
+
/**
* cgroup_css - obtain a cgroup's css for the specified subsystem
* @cgrp: the cgroup of interest
@@ -260,9 +269,9 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
if (!(cgrp->root->subsys_mask & (1 << ss->id)))
return NULL;

- while (cgrp->parent &&
- !(cgrp->parent->child_subsys_mask & (1 << ss->id)))
- cgrp = cgrp->parent;
+ while (cgroup_parent(cgrp) &&
+ !(cgroup_parent(cgrp)->child_subsys_mask & (1 << ss->id)))
+ cgrp = cgroup_parent(cgrp);

return cgroup_css(cgrp, ss);
}
@@ -307,7 +316,7 @@ bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor)
while (cgrp) {
if (cgrp == ancestor)
return true;
- cgrp = cgrp->parent;
+ cgrp = cgroup_parent(cgrp);
}
return false;
}
@@ -454,7 +463,7 @@ static void cgroup_update_populated(struct cgroup *cgrp, bool populated)

if (cgrp->populated_kn)
kernfs_notify(cgrp->populated_kn);
- cgrp = cgrp->parent;
+ cgrp = cgroup_parent(cgrp);
} while (cgrp);
}

@@ -2017,7 +2026,7 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
* Except for the root, child_subsys_mask must be zero for a cgroup
* with tasks so that child cgroups don't compete against tasks.
*/
- if (dst_cgrp && cgroup_on_dfl(dst_cgrp) && dst_cgrp->parent &&
+ if (dst_cgrp && cgroup_on_dfl(dst_cgrp) && cgroup_parent(dst_cgrp) &&
dst_cgrp->child_subsys_mask)
return -EBUSY;

@@ -2426,7 +2435,7 @@ static int cgroup_controllers_show(struct seq_file *seq, void *v)
{
struct cgroup *cgrp = seq_css(seq)->cgroup;

- cgroup_print_ss_mask(seq, cgrp->parent->child_subsys_mask);
+ cgroup_print_ss_mask(seq, cgroup_parent(cgrp)->child_subsys_mask);
return 0;
}

@@ -2609,8 +2618,8 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,

/* unavailable or not enabled on the parent? */
if (!(cgrp_dfl_root.subsys_mask & (1 << ssid)) ||
- (cgrp->parent &&
- !(cgrp->parent->child_subsys_mask & (1 << ssid)))) {
+ (cgroup_parent(cgrp) &&
+ !(cgroup_parent(cgrp)->child_subsys_mask & (1 << ssid)))) {
ret = -ENOENT;
goto out_unlock;
}
@@ -2639,7 +2648,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
* Except for the root, child_subsys_mask must be zero for a cgroup
* with tasks so that child cgroups don't compete against tasks.
*/
- if (enable && cgrp->parent && !list_empty(&cgrp->cset_links)) {
+ if (enable && cgroup_parent(cgrp) && !list_empty(&cgrp->cset_links)) {
ret = -EBUSY;
goto out_unlock;
}
@@ -2897,9 +2906,9 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
continue;
if ((cft->flags & CFTYPE_INSANE) && cgroup_sane_behavior(cgrp))
continue;
- if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
+ if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
continue;
- if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgrp->parent)
+ if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
continue;

if (is_add) {
@@ -4091,14 +4100,14 @@ static void css_free_work_fn(struct work_struct *work)
atomic_dec(&cgrp->root->nr_cgrps);
cgroup_pidlist_destroy_all(cgrp);

- if (cgrp->parent) {
+ if (cgroup_parent(cgrp)) {
/*
* We get a ref to the parent, and put the ref when
* this cgroup is being freed, so it's guaranteed
* that the parent won't be destroyed before its
* children.
*/
- cgroup_put(cgrp->parent);
+ cgroup_put(cgroup_parent(cgrp));
kernfs_put(cgrp->kn);
kfree(cgrp);
} else {
@@ -4162,8 +4171,8 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
css->ss = ss;
css->flags = 0;

- if (cgrp->parent) {
- css->parent = cgroup_css(cgrp->parent, ss);
+ if (cgroup_parent(cgrp)) {
+ css->parent = cgroup_css(cgroup_parent(cgrp), ss);
css_get(css->parent);
}

@@ -4217,7 +4226,7 @@ static void offline_css(struct cgroup_subsys_state *css)
*/
static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
{
- struct cgroup *parent = cgrp->parent;
+ struct cgroup *parent = cgroup_parent(cgrp);
struct cgroup_subsys_state *css;
int err;

@@ -4250,7 +4259,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
goto err_clear_dir;

if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
- parent->parent) {
+ cgroup_parent(parent)) {
pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
current->comm, current->pid, ss->name);
if (!strcmp(ss->name, "memory"))
@@ -4308,7 +4317,6 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,

init_cgroup_housekeeping(cgrp);

- cgrp->parent = parent;
cgrp->self.parent = &parent->self;
cgrp->root = root;

@@ -4335,7 +4343,7 @@ 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, &cgrp->parent->children);
+ list_add_tail_rcu(&cgrp->sibling, &cgroup_parent(cgrp)->children);
atomic_inc(&root->nr_cgrps);
cgroup_get(parent);

@@ -4530,8 +4538,8 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
*/
kernfs_remove(cgrp->kn);

- set_bit(CGRP_RELEASABLE, &cgrp->parent->flags);
- check_for_release(cgrp->parent);
+ set_bit(CGRP_RELEASABLE, &cgroup_parent(cgrp)->flags);
+ check_for_release(cgroup_parent(cgrp));

/* put the base reference */
percpu_ref_kill(&cgrp->self.refcnt);
--
1.9.0