cgroup: implement cgroup->e_csets[]

On the default unified hierarchy, a cgroup may be associated with
csses of its ancestors, which means that a css of a given cgroup may
be associated with css_sets of descendant cgroups.  This means that we
can't walk all tasks associated with a css by iterating the css_sets
associated with the cgroup as there are css_sets which are pointing to
the css but linked on the descendants.

This patch adds per-subsystem list heads cgroup->e_csets[].  Any
css_set which is pointing to a css is linked to
css->cgroup->e_csets[$SUBSYS_ID] through
css_set->e_cset_node[$SUBSYS_ID].  The lists are protected by
css_set_rwsem and will allow us to walk all css_sets associated with a
given css so that we can find out all associated tasks.

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 1b5b2fe..33a0043 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -187,6 +187,15 @@ struct cgroup {
         */
        struct list_head cset_links;
 
+       /*
+        * On the default hierarchy, a css_set for a cgroup with some
+        * susbsys disabled will point to css's which are associated with
+        * the closest ancestor which has the subsys enabled.  The
+        * following lists all css_sets which point to this cgroup's css
+        * for the given subsystem.
+        */
+       struct list_head e_csets[CGROUP_SUBSYS_COUNT];
+
        /*
         * Linked list running through all cgroups that can
         * potentially be reaped by the release agent. Protected by
@@ -369,6 +378,15 @@ struct css_set {
        struct cgroup *mg_src_cgrp;
        struct css_set *mg_dst_cset;
 
+       /*
+        * On the default hierarhcy, ->subsys[ssid] may point to a css
+        * attached to an ancestor instead of the cgroup this css_set is
+        * associated with.  The following node is anchored at
+        * ->subsys[ssid]->cgroup->e_csets[ssid] and provides a way to
+        * iterate through all css's attached to a given cgroup.
+        */
+       struct list_head e_cset_node[CGROUP_SUBSYS_COUNT];
+
        /* For RCU-protected deletion */
        struct rcu_head rcu_head;
 };

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4eb2dd1..37d9662 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -425,6 +425,8 @@ static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
 static void put_css_set_locked(struct css_set *cset, bool taskexit)
 {
        struct cgrp_cset_link *link, *tmp_link;
+       struct cgroup_subsys *ss;
+       int ssid;
 
        lockdep_assert_held(&css_set_rwsem);
 
@@ -432,6 +434,8 @@ static void put_css_set_locked(struct css_set *cset, bool taskexit)
                return;
 
        /* This css_set is dead. unlink it and release cgroup refcounts */
+       for_each_subsys(ss, ssid)
+               list_del(&cset->e_cset_node[ssid]);
        hash_del(&cset->hlist);
        css_set_count--;
 
@@ -673,7 +677,9 @@ static struct css_set *find_css_set(struct css_set *old_cset,
        struct css_set *cset;
        struct list_head tmp_links;
        struct cgrp_cset_link *link;
+       struct cgroup_subsys *ss;
        unsigned long key;
+       int ssid;
 
        lockdep_assert_held(&cgroup_mutex);
 
@@ -724,10 +730,14 @@ static struct css_set *find_css_set(struct css_set *old_cset,
 
        css_set_count++;
 
-       /* Add this cgroup group to the hash table */
+       /* Add @cset to the hash table */
        key = css_set_hash(cset->subsys);
        hash_add(css_set_table, &cset->hlist, key);
 
+       for_each_subsys(ss, ssid)
+               list_add_tail(&cset->e_cset_node[ssid],
+                             &cset->subsys[ssid]->cgroup->e_csets[ssid]);
+
        up_write(&css_set_rwsem);
 
        return cset;
@@ -1028,7 +1038,7 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
                             unsigned long ss_mask)
 {
        struct cgroup_subsys *ss;
-       int ssid, ret;
+       int ssid, i, ret;
 
        lockdep_assert_held(&cgroup_tree_mutex);
        lockdep_assert_held(&cgroup_mutex);
@@ -1081,6 +1091,7 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
        for_each_subsys(ss, ssid) {
                struct cgroup_root *src_root;
                struct cgroup_subsys_state *css;
+               struct css_set *cset;
 
                if (!(ss_mask & (1 << ssid)))
                        continue;
@@ -1095,6 +1106,12 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
                ss->root = dst_root;
                css->cgroup = &dst_root->cgrp;
 
+               down_write(&css_set_rwsem);
+               hash_for_each(css_set_table, i, cset, hlist)
+                       list_move_tail(&cset->e_cset_node[ss->id],
+                                      &dst_root->cgrp.e_csets[ss->id]);
+               up_write(&css_set_rwsem);
+
                src_root->subsys_mask &= ~(1 << ssid);
                src_root->cgrp.child_subsys_mask &= ~(1 << ssid);
 
@@ -1417,6 +1434,9 @@ out_unlock:
 
 static void init_cgroup_housekeeping(struct cgroup *cgrp)
 {
+       struct cgroup_subsys *ss;
+       int ssid;
+
        atomic_set(&cgrp->refcnt, 1);
        INIT_LIST_HEAD(&cgrp->sibling);
        INIT_LIST_HEAD(&cgrp->children);
@@ -1425,6 +1445,9 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
        INIT_LIST_HEAD(&cgrp->pidlists);
        mutex_init(&cgrp->pidlist_mutex);
        cgrp->dummy_css.cgroup = cgrp;
+
+       for_each_subsys(ss, ssid)
+               INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
 }
 
 static void init_cgroup_root(struct cgroup_root *root,
@@ -4249,6 +4272,9 @@ int __init cgroup_init(void)
                if (!ss->early_init)
                        cgroup_init_subsys(ss);
 
+               list_add_tail(&init_css_set.e_cset_node[ssid],
+                             &cgrp_dfl_root.cgrp.e_csets[ssid]);
+
                /*
                 * cftype registration needs kmalloc and can't be done
                 * during early_init.  Register base cftypes separately.