cgroup: add css_parent()
Currently, controllers have to explicitly follow the cgroup hierarchy
to find the parent of a given css. cgroup is moving towards using
cgroup_subsys_state as the main controller interface construct, so
let's provide a way to climb the hierarchy using just csses.
This patch implements css_parent() which, given a css, returns its
parent. The function is guarnateed to valid non-NULL parent css as
long as the target css is not at the top of the hierarchy.
freezer, cpuset, cpu, cpuacct, hugetlb, memory, net_cls and devices
are converted to use css_parent() instead of accessing cgroup->parent
directly.
* __parent_ca() is dropped from cpuacct and its usage is replaced with
parent_ca(). The only difference between the two was NULL test on
cgroup->parent which is now embedded in css_parent() making the
distinction moot. Note that eventually a css->parent field will be
added to css and the NULL check in css_parent() will go away.
This patch shouldn't cause any behavior differences.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 1db686e..657a73c 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -62,11 +62,7 @@
static struct freezer *parent_freezer(struct freezer *freezer)
{
- struct cgroup *pcg = freezer->css.cgroup->parent;
-
- if (pcg)
- return cgroup_freezer(pcg);
- return NULL;
+ return css_freezer(css_parent(&freezer->css));
}
bool cgroup_freezing(struct task_struct *task)
@@ -234,7 +230,7 @@
* The root cgroup is non-freezable, so we can skip the
* following check.
*/
- if (!freezer->css.cgroup->parent)
+ if (!parent_freezer(freezer))
goto out;
spin_lock_irq(&freezer->lock);
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 6e9cbdd..259a4af 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -133,11 +133,7 @@
static inline struct cpuset *parent_cs(struct cpuset *cs)
{
- struct cgroup *pcgrp = cs->css.cgroup->parent;
-
- if (pcgrp)
- return cgroup_cs(pcgrp);
- return NULL;
+ return css_cs(css_parent(&cs->css));
}
#ifdef CONFIG_NUMA
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5bccb02..7a10742 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7114,13 +7114,10 @@
static int cpu_cgroup_css_online(struct cgroup *cgrp)
{
struct task_group *tg = cgroup_tg(cgrp);
- struct task_group *parent;
+ struct task_group *parent = css_tg(css_parent(&tg->css));
- if (!cgrp->parent)
- return 0;
-
- parent = cgroup_tg(cgrp->parent);
- sched_online_group(tg, parent);
+ if (parent)
+ sched_online_group(tg, parent);
return 0;
}
diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 8ccfa10..f6926a1 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -50,16 +50,9 @@
return css_ca(task_css(tsk, cpuacct_subsys_id));
}
-static inline struct cpuacct *__parent_ca(struct cpuacct *ca)
-{
- return cgroup_ca(ca->css.cgroup->parent);
-}
-
static inline struct cpuacct *parent_ca(struct cpuacct *ca)
{
- if (!ca->css.cgroup->parent)
- return NULL;
- return cgroup_ca(ca->css.cgroup->parent);
+ return css_ca(css_parent(&ca->css));
}
static DEFINE_PER_CPU(u64, root_cpuacct_cpuusage);
@@ -284,7 +277,7 @@
while (ca != &root_cpuacct) {
kcpustat = this_cpu_ptr(ca->cpustat);
kcpustat->cpustat[index] += val;
- ca = __parent_ca(ca);
+ ca = parent_ca(ca);
}
rcu_read_unlock();
}