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From: Tejun Heo
Date: Tue May 13 2014 - 14:47:01 EST

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cgroup in general is moving towards using cgroup_subsys_state as the
fundamental structural component and css_parent() was introduced to
convert from using cgroup->parent to css->parent. It was quite some
time ago and we're moving forward with making css more prominent.

This patch drops the trivial wrapper css_parent() and let the users
dereference css->parent. While at it, explicitly mark fields of css
which are public and immutable.

v2: New usage from device_cgroup.c converted.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
Acked-by: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Li Zefan <lizefan@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
---
block/blk-cgroup.h | 2 +-
include/linux/cgroup.h | 29 +++++++++++------------------
kernel/cgroup.c | 8 ++++----
kernel/cgroup_freezer.c | 2 +-
kernel/cpuset.c | 2 +-
kernel/sched/core.c | 2 +-
kernel/sched/cpuacct.c | 2 +-
mm/hugetlb_cgroup.c | 2 +-
mm/memcontrol.c | 14 +++++++-------
net/core/netclassid_cgroup.c | 2 +-
net/core/netprio_cgroup.c | 2 +-
security/device_cgroup.c | 8 ++++----
12 files changed, 34 insertions(+), 41 deletions(-)

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 371fe8e..d692b29 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -204,7 +204,7 @@ static inline struct blkcg *bio_blkcg(struct bio *bio)
*/
static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
{
- return css_to_blkcg(css_parent(&blkcg->css));
+ return css_to_blkcg(blkcg->css.parent);
}

/**
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 76dadd77..88c4d03 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -48,22 +48,28 @@ enum cgroup_subsys_id {
};
#undef SUBSYS

-/* Per-subsystem/per-cgroup state maintained by the system. */
+/*
+ * Per-subsystem/per-cgroup state maintained by the system. This is the
+ * fundamental structural building block that controllers deal with.
+ *
+ * Fields marked with "PI:" are public and immutable and may be accessed
+ * directly without synchronization.
+ */
struct cgroup_subsys_state {
- /* the cgroup that this css is attached to */
+ /* PI: the cgroup that this css is attached to */
struct cgroup *cgroup;

- /* the cgroup subsystem that this css is attached to */
+ /* PI: the cgroup subsystem that this css is attached to */
struct cgroup_subsys *ss;

/* reference count - access via css_[try]get() and css_put() */
struct percpu_ref refcnt;

- /* the parent css */
+ /* PI: the parent css */
struct cgroup_subsys_state *parent;

/*
- * Subsys-unique ID. 0 is unused and root is always 1. The
+ * PI: Subsys-unique ID. 0 is unused and root is always 1. The
* matching css can be looked up using css_from_id().
*/
int id;
@@ -665,19 +671,6 @@ struct cgroup_subsys {
#undef SUBSYS

/**
- * css_parent - find the parent css
- * @css: the target cgroup_subsys_state
- *
- * Return the parent css of @css. This function is guaranteed to return
- * non-NULL parent as long as @css isn't the root.
- */
-static inline
-struct cgroup_subsys_state *css_parent(struct cgroup_subsys_state *css)
-{
- return css->parent;
-}
-
-/**
* task_css_set_check - obtain a task's css_set with extra access conditions
* @task: the task to obtain css_set for
* @__c: extra condition expression to be passed to rcu_dereference_check()
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 365787f..321163a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3175,10 +3175,10 @@ css_next_descendant_pre(struct cgroup_subsys_state *pos,

/* no child, visit my or the closest ancestor's next sibling */
while (pos != root) {
- next = css_next_child(pos, css_parent(pos));
+ next = css_next_child(pos, pos->parent);
if (next)
return next;
- pos = css_parent(pos);
+ pos = pos->parent;
}

return NULL;
@@ -3260,12 +3260,12 @@ css_next_descendant_post(struct cgroup_subsys_state *pos,
return NULL;

/* if there's an unvisited sibling, visit its leftmost descendant */
- next = css_next_child(pos, css_parent(pos));
+ next = css_next_child(pos, pos->parent);
if (next)
return css_leftmost_descendant(next);

/* no sibling left, visit parent */
- return css_parent(pos);
+ return pos->parent;
}

static bool cgroup_has_live_children(struct cgroup *cgrp)
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 6b4e60e..a79e40f 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -59,7 +59,7 @@ static inline struct freezer *task_freezer(struct task_struct *task)

static struct freezer *parent_freezer(struct freezer *freezer)
{
- return css_freezer(css_parent(&freezer->css));
+ return css_freezer(freezer->css.parent);
}

bool cgroup_freezing(struct task_struct *task)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 2f4b08b..5b2a310 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -124,7 +124,7 @@ static inline struct cpuset *task_cs(struct task_struct *task)

static inline struct cpuset *parent_cs(struct cpuset *cs)
{
- return css_cs(css_parent(&cs->css));
+ return css_cs(cs->css.parent);
}

#ifdef CONFIG_NUMA
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 268a45e..ac61ad1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7586,7 +7586,7 @@ cpu_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
static int cpu_cgroup_css_online(struct cgroup_subsys_state *css)
{
struct task_group *tg = css_tg(css);
- struct task_group *parent = css_tg(css_parent(css));
+ struct task_group *parent = css_tg(css->parent);

if (parent)
sched_online_group(tg, parent);
diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index c143ee3..9cf350c 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -46,7 +46,7 @@ static inline struct cpuacct *task_ca(struct task_struct *tsk)

static inline struct cpuacct *parent_ca(struct cpuacct *ca)
{
- return css_ca(css_parent(&ca->css));
+ return css_ca(ca->css.parent);
}

static DEFINE_PER_CPU(u64, root_cpuacct_cpuusage);
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index a380681..493f758 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -52,7 +52,7 @@ static inline bool hugetlb_cgroup_is_root(struct hugetlb_cgroup *h_cg)
static inline struct hugetlb_cgroup *
parent_hugetlb_cgroup(struct hugetlb_cgroup *h_cg)
{
- return hugetlb_cgroup_from_css(css_parent(&h_cg->css));
+ return hugetlb_cgroup_from_css(h_cg->css.parent);
}

static inline bool hugetlb_cgroup_have_usage(struct hugetlb_cgroup *h_cg)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b638a79..a5e0417 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1540,7 +1540,7 @@ static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
/* root ? */
- if (!css_parent(&memcg->css))
+ if (!memcg->css.parent)
return vm_swappiness;

return memcg->swappiness;
@@ -4909,7 +4909,7 @@ static int mem_cgroup_hierarchy_write(struct cgroup_subsys_state *css,
{
int retval = 0;
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
- struct mem_cgroup *parent_memcg = mem_cgroup_from_css(css_parent(&memcg->css));
+ struct mem_cgroup *parent_memcg = mem_cgroup_from_css(memcg->css.parent);

mutex_lock(&memcg_create_mutex);

@@ -5207,8 +5207,8 @@ static void memcg_get_hierarchical_limit(struct mem_cgroup *memcg,
if (!memcg->use_hierarchy)
goto out;

- while (css_parent(&memcg->css)) {
- memcg = mem_cgroup_from_css(css_parent(&memcg->css));
+ while (memcg->css.parent) {
+ memcg = mem_cgroup_from_css(memcg->css.parent);
if (!memcg->use_hierarchy)
break;
tmp = res_counter_read_u64(&memcg->res, RES_LIMIT);
@@ -5443,7 +5443,7 @@ static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
struct cftype *cft, u64 val)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
- struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(&memcg->css));
+ struct mem_cgroup *parent = mem_cgroup_from_css(memcg->css.parent);

if (val > 100 || !parent)
return -EINVAL;
@@ -5790,7 +5790,7 @@ static int mem_cgroup_oom_control_write(struct cgroup_subsys_state *css,
struct cftype *cft, u64 val)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
- struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(&memcg->css));
+ struct mem_cgroup *parent = mem_cgroup_from_css(memcg->css.parent);

/* cannot set to root cgroup and only 0 and 1 are allowed */
if (!parent || !((val == 0) || (val == 1)))
@@ -6407,7 +6407,7 @@ static int
mem_cgroup_css_online(struct cgroup_subsys_state *css)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
- struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(css));
+ struct mem_cgroup *parent = mem_cgroup_from_css(css->parent);

if (css->id > MEM_CGROUP_ID_MAX)
return -ENOSPC;
diff --git a/net/core/netclassid_cgroup.c b/net/core/netclassid_cgroup.c
index 22931e1..30d903b 100644
--- a/net/core/netclassid_cgroup.c
+++ b/net/core/netclassid_cgroup.c
@@ -42,7 +42,7 @@ cgrp_css_alloc(struct cgroup_subsys_state *parent_css)
static int cgrp_css_online(struct cgroup_subsys_state *css)
{
struct cgroup_cls_state *cs = css_cls_state(css);
- struct cgroup_cls_state *parent = css_cls_state(css_parent(css));
+ struct cgroup_cls_state *parent = css_cls_state(css->parent);

if (parent)
cs->classid = parent->classid;
diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index b990cef..2f385b9 100644
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c
@@ -140,7 +140,7 @@ cgrp_css_alloc(struct cgroup_subsys_state *parent_css)

static int cgrp_css_online(struct cgroup_subsys_state *css)
{
- struct cgroup_subsys_state *parent_css = css_parent(css);
+ struct cgroup_subsys_state *parent_css = css->parent;
struct net_device *dev;
int ret = 0;

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 7dbac40..ce14a31 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -182,7 +182,7 @@ static inline bool is_devcg_online(const struct dev_cgroup *devcg)
static int devcgroup_online(struct cgroup_subsys_state *css)
{
struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
- struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css_parent(css));
+ struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
int ret = 0;

mutex_lock(&devcgroup_mutex);
@@ -455,7 +455,7 @@ static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
static int parent_has_perm(struct dev_cgroup *childcg,
struct dev_exception_item *ex)
{
- struct dev_cgroup *parent = css_to_devcgroup(css_parent(&childcg->css));
+ struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);

if (!parent)
return 1;
@@ -476,7 +476,7 @@ static int parent_has_perm(struct dev_cgroup *childcg,
static bool parent_allows_removal(struct dev_cgroup *childcg,
struct dev_exception_item *ex)
{
- struct dev_cgroup *parent = css_to_devcgroup(css_parent(&childcg->css));
+ struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);

if (!parent)
return true;
@@ -614,7 +614,7 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
char temp[12]; /* 11 + 1 characters needed for a u32 */
int count, rc = 0;
struct dev_exception_item ex;
- struct dev_cgroup *parent = css_to_devcgroup(css_parent(&devcgroup->css));
+ struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);

if (!capable(CAP_SYS_ADMIN))
return -EPERM;
--
1.9.0

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