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Subject[PATCH 03/12] cgroup: implement cgroup->e_csets[]
Date
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>
---
include/linux/cgroup.h | 18 ++++++++++++++++++
kernel/cgroup.c | 30 ++++++++++++++++++++++++++++--
2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e351a18..e902eee 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -188,6 +188,15 @@ 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
* release_list_lock
@@ -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 ae1fe5a..2899a6f 100644
--- 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,
@@ -4224,6 +4247,9 @@ 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.
--
1.8.5.3


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