cgroup: remove cgroup->parent

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>
Acked-by: Li Zefan <lizefan@huawei.com>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 2549493d518d0dcb07358189fe82fa81039db7c8..fd538f4c2bb648b70aeae77552403260b9ce04a0 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -178,7 +178,6 @@ 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 929bbbc539e9dfe546dfe77e6d057a0faed503e8..8c67a739aea46ec70d3bfd0ed2e4e44b5197f159 100644 (file)
--- 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);
 }
 
@@ -2018,7 +2027,7 @@ 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;
 
@@ -2427,7 +2436,7 @@ 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;
 }
 
@@ -2610,8 +2619,8 @@ 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;
                        }
@@ -2640,7 +2649,7 @@ 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;
        }
@@ -2898,9 +2907,9 @@ 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) {
@@ -4092,14 +4101,14 @@ 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 {
@@ -4163,8 +4172,8 @@ 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);
        }
 
@@ -4218,7 +4227,7 @@ 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;
 
@@ -4251,7 +4260,7 @@ 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"))
@@ -4309,7 +4318,6 @@ 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;
 
@@ -4336,7 +4344,7 @@ 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);
 
@@ -4531,8 +4539,8 @@ 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);