[PATCH 03/11] cgroup: bring some sanity to naming around cg_cgroup_link

From: Tejun Heo
Date: Thu Jun 13 2013 - 00:07:46 EST

cgroups and css_sets are mapped M:N and this M:N mapping is
represented by struct cg_cgroup_link which forms linked lists on both
sides. The naming around this mapping is already confusing and struct
cg_cgroup_link exacerbates the situation quite a bit.

>From cgroup side, it starts off ->css_sets and runs through
->cgrp_link_list. From css_set side, it starts off ->cg_links and
runs through ->cg_link_list. This is rather reversed as
cgrp_link_list is used to iterate css_sets and cg_link_list cgroups.
Also, this is the only place which is still using the confusing "cg"
for css_sets. This patch cleans it up a bit.

* s/cgroup->css_sets/cgroup->cset_links/
s/css_set->cg_links/css_set->cgrp_links/
s/cgroup_iter->cg_link/cgroup_iter->cset_link/

* s/cg_cgroup_link/cgrp_cset_link/

* s/cgrp_cset_link->cg/cgrp_cset_link->cset/
s/cgrp_cset_link->cgrp_link_list/cgrp_cset_link->cset_link/
s/cgrp_cset_link->cg_link_list/cgrp_cset_link->cgrp_link/

* s/init_css_set_link/init_cgrp_cset_link/
s/free_cg_links/free_cgrp_cset_links/
s/allocate_cg_links/allocate_cgrp_cset_links/

* s/cgl[12]/link[12]/ in compare_css_sets()

* s/saved_link/tmp_link/ s/tmp/tmp_links/ and a couple similar
adustments.

* Comment and whiteline adjustments.

After the changes, we have

list_for_each_entry(link, &cont->cset_links, cset_link) {
struct css_set *cset = link->cset;

instead of

list_for_each_entry(link, &cont->css_sets, cgrp_link_list) {
struct css_set *cset = link->cg;

This patch is purely cosmetic.

v2: Fix broken sentences in the patch description.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
include/linux/cgroup.h | 15 ++--
kernel/cgroup.c | 226 ++++++++++++++++++++++++-------------------------
2 files changed, 120 insertions(+), 121 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 5830592..0e32855 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -215,10 +215,10 @@ struct cgroup {
struct cgroupfs_root *root;

/*
- * List of cg_cgroup_links pointing at css_sets with
- * tasks in this cgroup. Protected by css_set_lock
+ * List of cgrp_cset_links pointing at css_sets with tasks in this
+ * cgroup. Protected by css_set_lock.
*/
- struct list_head css_sets;
+ struct list_head cset_links;

struct list_head allcg_node; /* cgroupfs_root->allcg_list */
struct list_head cft_q_node; /* used during cftype add/rm */
@@ -365,11 +365,10 @@ struct css_set {
struct list_head tasks;

/*
- * List of cg_cgroup_link objects on link chains from
- * cgroups referenced from this css_set. Protected by
- * css_set_lock
+ * List of cgrp_cset_links pointing at cgroups referenced from this
+ * css_set. Protected by css_set_lock.
*/
- struct list_head cg_links;
+ struct list_head cgrp_links;

/*
* Set of subsystem states, one for each subsystem. This array
@@ -792,7 +791,7 @@ struct cgroup *cgroup_next_descendant_post(struct cgroup *pos,

/* A cgroup_iter should be treated as an opaque object */
struct cgroup_iter {
- struct list_head *cg_link;
+ struct list_head *cset_link;
struct list_head *task;
};

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e7f6845..0b5cd0e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -315,20 +315,24 @@ static void cgroup_release_agent(struct work_struct *work);
static DECLARE_WORK(release_agent_work, cgroup_release_agent);
static void check_for_release(struct cgroup *cgrp);

-/* Link structure for associating css_set objects with cgroups */
-struct cg_cgroup_link {
- /*
- * List running through cg_cgroup_links associated with a
- * cgroup, anchored on cgroup->css_sets
- */
- struct list_head cgrp_link_list;
- struct cgroup *cgrp;
- /*
- * List running through cg_cgroup_links pointing at a
- * single css_set object, anchored on css_set->cg_links
- */
- struct list_head cg_link_list;
- struct css_set *cg;
+/*
+ * A cgroup can be associated with multiple css_sets as different tasks may
+ * belong to different cgroups on different hierarchies. In the other
+ * direction, a css_set is naturally associated with multiple cgroups.
+ * This M:N relationship is represented by the following link structure
+ * which exists for each association and allows traversing the associations
+ * from both sides.
+ */
+struct cgrp_cset_link {
+ /* the cgroup and css_set this link associates */
+ struct cgroup *cgrp;
+ struct css_set *cset;
+
+ /* list of cgrp_cset_links anchored at cgrp->cset_links */
+ struct list_head cset_link;
+
+ /* list of cgrp_cset_links anchored at css_set->cgrp_links */
+ struct list_head cgrp_link;
};

/* The default css_set - used by init and its children prior to any
@@ -339,7 +343,7 @@ struct cg_cgroup_link {
*/

static struct css_set init_css_set;
-static struct cg_cgroup_link init_css_set_link;
+static struct cgrp_cset_link init_cgrp_cset_link;

static int cgroup_init_idr(struct cgroup_subsys *ss,
struct cgroup_subsys_state *css);
@@ -378,8 +382,7 @@ static int use_task_css_set_links __read_mostly;

static void __put_css_set(struct css_set *cset, int taskexit)
{
- struct cg_cgroup_link *link;
- struct cg_cgroup_link *saved_link;
+ struct cgrp_cset_link *link, *tmp_link;

/*
* Ensure that the refcount doesn't hit zero while any readers
@@ -398,12 +401,11 @@ static void __put_css_set(struct css_set *cset, int taskexit)
hash_del(&cset->hlist);
css_set_count--;

- list_for_each_entry_safe(link, saved_link, &cset->cg_links,
- cg_link_list) {
+ list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
struct cgroup *cgrp = link->cgrp;

- list_del(&link->cg_link_list);
- list_del(&link->cgrp_link_list);
+ list_del(&link->cset_link);
+ list_del(&link->cgrp_link);

/*
* We may not be holding cgroup_mutex, and if cgrp->count is
@@ -475,26 +477,26 @@ static bool compare_css_sets(struct css_set *cset,
* candidates.
*/

- l1 = &cset->cg_links;
- l2 = &old_cset->cg_links;
+ l1 = &cset->cgrp_links;
+ l2 = &old_cset->cgrp_links;
while (1) {
- struct cg_cgroup_link *cgl1, *cgl2;
+ struct cgrp_cset_link *link1, *link2;
struct cgroup *cgrp1, *cgrp2;

l1 = l1->next;
l2 = l2->next;
/* See if we reached the end - both lists are equal length. */
- if (l1 == &cset->cg_links) {
- BUG_ON(l2 != &old_cset->cg_links);
+ if (l1 == &cset->cgrp_links) {
+ BUG_ON(l2 != &old_cset->cgrp_links);
break;
} else {
- BUG_ON(l2 == &old_cset->cg_links);
+ BUG_ON(l2 == &old_cset->cgrp_links);
}
/* Locate the cgroups associated with these links. */
- cgl1 = list_entry(l1, struct cg_cgroup_link, cg_link_list);
- cgl2 = list_entry(l2, struct cg_cgroup_link, cg_link_list);
- cgrp1 = cgl1->cgrp;
- cgrp2 = cgl2->cgrp;
+ link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
+ link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
+ cgrp1 = link1->cgrp;
+ cgrp2 = link2->cgrp;
/* Hierarchies should be linked in the same order. */
BUG_ON(cgrp1->root != cgrp2->root);

@@ -569,61 +571,64 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset,
return NULL;
}

-static void free_cg_links(struct list_head *tmp)
+static void free_cgrp_cset_links(struct list_head *links_to_free)
{
- struct cg_cgroup_link *link;
- struct cg_cgroup_link *saved_link;
+ struct cgrp_cset_link *link, *tmp_link;

- list_for_each_entry_safe(link, saved_link, tmp, cgrp_link_list) {
- list_del(&link->cgrp_link_list);
+ list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
+ list_del(&link->cset_link);
kfree(link);
}
}

-/*
- * allocate_cg_links() allocates "count" cg_cgroup_link structures
- * and chains them on tmp through their cgrp_link_list fields. Returns 0 on
- * success or a negative error
+/**
+ * allocate_cgrp_cset_links - allocate cgrp_cset_links
+ * @count: the number of links to allocate
+ * @tmp_links: list_head the allocated links are put on
+ *
+ * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
+ * through ->cset_link. Returns 0 on success or -errno.
*/
-static int allocate_cg_links(int count, struct list_head *tmp)
+static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
{
- struct cg_cgroup_link *link;
+ struct cgrp_cset_link *link;
int i;
- INIT_LIST_HEAD(tmp);
+
+ INIT_LIST_HEAD(tmp_links);
+
for (i = 0; i < count; i++) {
link = kmalloc(sizeof(*link), GFP_KERNEL);
if (!link) {
- free_cg_links(tmp);
+ free_cgrp_cset_links(tmp_links);
return -ENOMEM;
}
- list_add(&link->cgrp_link_list, tmp);
+ list_add(&link->cset_link, tmp_links);
}
return 0;
}

/**
* link_css_set - a helper function to link a css_set to a cgroup
- * @tmp_cg_links: cg_cgroup_link objects allocated by allocate_cg_links()
+ * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
* @cset: the css_set to be linked
* @cgrp: the destination cgroup
*/
-static void link_css_set(struct list_head *tmp_cg_links,
- struct css_set *cset, struct cgroup *cgrp)
+static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
+ struct cgroup *cgrp)
{
- struct cg_cgroup_link *link;
+ struct cgrp_cset_link *link;

- BUG_ON(list_empty(tmp_cg_links));
- link = list_first_entry(tmp_cg_links, struct cg_cgroup_link,
- cgrp_link_list);
- link->cg = cset;
+ BUG_ON(list_empty(tmp_links));
+ link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
+ link->cset = cset;
link->cgrp = cgrp;
atomic_inc(&cgrp->count);
- list_move(&link->cgrp_link_list, &cgrp->css_sets);
+ list_move(&link->cset_link, &cgrp->cset_links);
/*
* Always add links to the tail of the list so that the list
* is sorted by order of hierarchy creation
*/
- list_add_tail(&link->cg_link_list, &cset->cg_links);
+ list_add_tail(&link->cgrp_link, &cset->cgrp_links);
}

/*
@@ -638,10 +643,8 @@ static struct css_set *find_css_set(struct css_set *old_cset,
{
struct css_set *cset;
struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
-
- struct list_head tmp_cg_links;
-
- struct cg_cgroup_link *link;
+ struct list_head tmp_links;
+ struct cgrp_cset_link *link;
unsigned long key;

/* First see if we already have a cgroup group that matches
@@ -659,14 +662,14 @@ static struct css_set *find_css_set(struct css_set *old_cset,
if (!cset)
return NULL;

- /* Allocate all the cg_cgroup_link objects that we'll need */
- if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
+ /* Allocate all the cgrp_cset_link objects that we'll need */
+ if (allocate_cgrp_cset_links(root_count, &tmp_links) < 0) {
kfree(cset);
return NULL;
}

atomic_set(&cset->refcount, 1);
- INIT_LIST_HEAD(&cset->cg_links);
+ INIT_LIST_HEAD(&cset->cgrp_links);
INIT_LIST_HEAD(&cset->tasks);
INIT_HLIST_NODE(&cset->hlist);

@@ -676,14 +679,15 @@ static struct css_set *find_css_set(struct css_set *old_cset,

write_lock(&css_set_lock);
/* Add reference counts and links from the new css_set. */
- list_for_each_entry(link, &old_cset->cg_links, cg_link_list) {
+ list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
struct cgroup *c = link->cgrp;
+
if (c->root == cgrp->root)
c = cgrp;
- link_css_set(&tmp_cg_links, cset, c);
+ link_css_set(&tmp_links, cset, c);
}

- BUG_ON(!list_empty(&tmp_cg_links));
+ BUG_ON(!list_empty(&tmp_links));

css_set_count++;

@@ -717,9 +721,11 @@ static struct cgroup *task_cgroup_from_root(struct task_struct *task,
if (cset == &init_css_set) {
res = &root->top_cgroup;
} else {
- struct cg_cgroup_link *link;
- list_for_each_entry(link, &cset->cg_links, cg_link_list) {
+ struct cgrp_cset_link *link;
+
+ list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
struct cgroup *c = link->cgrp;
+
if (c->root == root) {
res = c;
break;
@@ -1405,7 +1411,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
INIT_LIST_HEAD(&cgrp->sibling);
INIT_LIST_HEAD(&cgrp->children);
INIT_LIST_HEAD(&cgrp->files);
- INIT_LIST_HEAD(&cgrp->css_sets);
+ INIT_LIST_HEAD(&cgrp->cset_links);
INIT_LIST_HEAD(&cgrp->allcg_node);
INIT_LIST_HEAD(&cgrp->release_list);
INIT_LIST_HEAD(&cgrp->pidlists);
@@ -1604,7 +1610,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
BUG_ON(!root);
if (root == opts.new_root) {
/* We used the new root structure, so this is a new hierarchy */
- struct list_head tmp_cg_links;
+ struct list_head tmp_links;
struct cgroup *root_cgrp = &root->top_cgroup;
struct cgroupfs_root *existing_root;
const struct cred *cred;
@@ -1636,7 +1642,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
* that's us. The worst that can happen is that we
* have some link structures left over
*/
- ret = allocate_cg_links(css_set_count, &tmp_cg_links);
+ ret = allocate_cgrp_cset_links(css_set_count, &tmp_links);
if (ret)
goto unlock_drop;

@@ -1646,7 +1652,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,

ret = rebind_subsystems(root, root->subsys_mask);
if (ret == -EBUSY) {
- free_cg_links(&tmp_cg_links);
+ free_cgrp_cset_links(&tmp_links);
goto unlock_drop;
}
/*
@@ -1668,10 +1674,10 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
* the css_set objects */
write_lock(&css_set_lock);
hash_for_each(css_set_table, i, cset, hlist)
- link_css_set(&tmp_cg_links, cset, root_cgrp);
+ link_css_set(&tmp_links, cset, root_cgrp);
write_unlock(&css_set_lock);

- free_cg_links(&tmp_cg_links);
+ free_cgrp_cset_links(&tmp_links);

BUG_ON(!list_empty(&root_cgrp->children));
BUG_ON(root->number_of_cgroups != 1);
@@ -1725,9 +1731,8 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
static void cgroup_kill_sb(struct super_block *sb) {
struct cgroupfs_root *root = sb->s_fs_info;
struct cgroup *cgrp = &root->top_cgroup;
+ struct cgrp_cset_link *link, *tmp_link;
int ret;
- struct cg_cgroup_link *link;
- struct cg_cgroup_link *saved_link;

BUG_ON(!root);

@@ -1743,15 +1748,14 @@ static void cgroup_kill_sb(struct super_block *sb) {
BUG_ON(ret);

/*
- * Release all the links from css_sets to this hierarchy's
+ * Release all the links from cset_links to this hierarchy's
* root cgroup
*/
write_lock(&css_set_lock);

- list_for_each_entry_safe(link, saved_link, &cgrp->css_sets,
- cgrp_link_list) {
- list_del(&link->cg_link_list);
- list_del(&link->cgrp_link_list);
+ list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
+ list_del(&link->cset_link);
+ list_del(&link->cgrp_link);
kfree(link);
}
write_unlock(&css_set_lock);
@@ -2911,12 +2915,11 @@ int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
int cgroup_task_count(const struct cgroup *cgrp)
{
int count = 0;
- struct cg_cgroup_link *link;
+ struct cgrp_cset_link *link;

read_lock(&css_set_lock);
- list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
- count += atomic_read(&link->cg->refcount);
- }
+ list_for_each_entry(link, &cgrp->cset_links, cset_link)
+ count += atomic_read(&link->cset->refcount);
read_unlock(&css_set_lock);
return count;
}
@@ -2925,24 +2928,23 @@ int cgroup_task_count(const struct cgroup *cgrp)
* Advance a list_head iterator. The iterator should be positioned at
* the start of a css_set
*/
-static void cgroup_advance_iter(struct cgroup *cgrp,
- struct cgroup_iter *it)
+static void cgroup_advance_iter(struct cgroup *cgrp, struct cgroup_iter *it)
{
- struct list_head *l = it->cg_link;
- struct cg_cgroup_link *link;
+ struct list_head *l = it->cset_link;
+ struct cgrp_cset_link *link;
struct css_set *cset;

/* Advance to the next non-empty css_set */
do {
l = l->next;
- if (l == &cgrp->css_sets) {
- it->cg_link = NULL;
+ if (l == &cgrp->cset_links) {
+ it->cset_link = NULL;
return;
}
- link = list_entry(l, struct cg_cgroup_link, cgrp_link_list);
- cset = link->cg;
+ link = list_entry(l, struct cgrp_cset_link, cset_link);
+ cset = link->cset;
} while (list_empty(&cset->tasks));
- it->cg_link = l;
+ it->cset_link = l;
it->task = cset->tasks.next;
}

@@ -3163,7 +3165,7 @@ void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
cgroup_enable_task_cg_lists();

read_lock(&css_set_lock);
- it->cg_link = &cgrp->css_sets;
+ it->cset_link = &cgrp->cset_links;
cgroup_advance_iter(cgrp, it);
}

@@ -3172,16 +3174,16 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
{
struct task_struct *res;
struct list_head *l = it->task;
- struct cg_cgroup_link *link;
+ struct cgrp_cset_link *link;

/* If the iterator cg is NULL, we have no tasks */
- if (!it->cg_link)
+ if (!it->cset_link)
return NULL;
res = list_entry(l, struct task_struct, cg_list);
/* Advance iterator to find next entry */
l = l->next;
- link = list_entry(it->cg_link, struct cg_cgroup_link, cgrp_link_list);
- if (l == &link->cg->tasks) {
+ link = list_entry(it->cset_link, struct cgrp_cset_link, cset_link);
+ if (l == &link->cset->tasks) {
/* We reached the end of this task list - move on to
* the next cg_cgroup_link */
cgroup_advance_iter(cgrp, it);
@@ -4628,7 +4630,7 @@ EXPORT_SYMBOL_GPL(cgroup_load_subsys);
*/
void cgroup_unload_subsys(struct cgroup_subsys *ss)
{
- struct cg_cgroup_link *link;
+ struct cgrp_cset_link *link;

BUG_ON(ss->module == NULL);

@@ -4657,8 +4659,8 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
* in loading, we need to pay our respects to the hashtable gods.
*/
write_lock(&css_set_lock);
- list_for_each_entry(link, &dummytop->css_sets, cgrp_link_list) {
- struct css_set *cset = link->cg;
+ list_for_each_entry(link, &dummytop->cset_links, cset_link) {
+ struct css_set *cset = link->cset;
unsigned long key;

hash_del(&cset->hlist);
@@ -4691,7 +4693,7 @@ int __init cgroup_init_early(void)
{
int i;
atomic_set(&init_css_set.refcount, 1);
- INIT_LIST_HEAD(&init_css_set.cg_links);
+ INIT_LIST_HEAD(&init_css_set.cgrp_links);
INIT_LIST_HEAD(&init_css_set.tasks);
INIT_HLIST_NODE(&init_css_set.hlist);
css_set_count = 1;
@@ -4699,12 +4701,10 @@ int __init cgroup_init_early(void)
root_count = 1;
init_task.cgroups = &init_css_set;

- init_css_set_link.cg = &init_css_set;
- init_css_set_link.cgrp = dummytop;
- list_add(&init_css_set_link.cgrp_link_list,
- &rootnode.top_cgroup.css_sets);
- list_add(&init_css_set_link.cg_link_list,
- &init_css_set.cg_links);
+ init_cgrp_cset_link.cset = &init_css_set;
+ init_cgrp_cset_link.cgrp = dummytop;
+ list_add(&init_cgrp_cset_link.cset_link, &rootnode.top_cgroup.cset_links);
+ list_add(&init_cgrp_cset_link.cgrp_link, &init_css_set.cgrp_links);

for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
@@ -5457,13 +5457,13 @@ static int current_css_set_cg_links_read(struct cgroup *cont,
struct cftype *cft,
struct seq_file *seq)
{
- struct cg_cgroup_link *link;
+ struct cgrp_cset_link *link;
struct css_set *cset;

read_lock(&css_set_lock);
rcu_read_lock();
cset = rcu_dereference(current->cgroups);
- list_for_each_entry(link, &cset->cg_links, cg_link_list) {
+ list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
struct cgroup *c = link->cgrp;
const char *name;

@@ -5484,11 +5484,11 @@ static int cgroup_css_links_read(struct cgroup *cont,
struct cftype *cft,
struct seq_file *seq)
{
- struct cg_cgroup_link *link;
+ struct cgrp_cset_link *link;

read_lock(&css_set_lock);
- list_for_each_entry(link, &cont->css_sets, cgrp_link_list) {
- struct css_set *cset = link->cg;
+ list_for_each_entry(link, &cont->cset_links, cset_link) {
+ struct css_set *cset = link->cset;
struct task_struct *task;
int count = 0;
seq_printf(seq, "css_set %p\n", cset);
--
1.8.2.1

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