BACKPORT: cgroup: misc changes

Misc trivial changes to prepare for future changes.  No functional
difference.

* Expose cgroup_get(), cgroup_tryget() and cgroup_parent().

* Implement task_dfl_cgroup() which dereferences css_set->dfl_cgrp.

* Rename cgroup_stats_show() to cgroup_stat_show() for consistency
  with the file name.

Signed-off-by: Tejun Heo <tj@kernel.org>

(cherry picked from commit 3e48930cc74f0c212ee1838f89ad0ca7fcf2fea1)

Conflicts:
        kernel/cgroup/cgroup.c

(1. manual merge because kernel/cgroup/cgroup.c is under kernel/cgroup.c
2. cgroup_stats_show change is skipped because the function dos not exist)

Bug: 111308141
Test: modified lmkd to use PSI and tested using lmkd_unit_test

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I756ee3dcf0d0f3da69cd1b58e644271625053538
Signed-off-by: Chatur27 <jasonbright2709@gmail.com>

2 files changed, 24 insertions, 20 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 812fb2609838..82962c5a7475 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -388,6 +388,16 @@ static inline void css_put_many(struct cgroup_subsys_state *css, unsigned int n)
 		percpu_ref_put_many(&css->refcnt, n);
 }
 
+static inline void cgroup_get(struct cgroup *cgrp)
+{
+	css_get(&cgrp->self);
+}
+
+static inline bool cgroup_tryget(struct cgroup *cgrp)
+{
+	return css_tryget(&cgrp->self);
+}
+
 static inline void cgroup_put(struct cgroup *cgrp)
 {
 	css_put(&cgrp->self);
@@ -506,6 +516,20 @@ static inline struct cgroup *task_cgroup(struct task_struct *task,
 	return task_css(task, subsys_id)->cgroup;
 }
 
+static inline struct cgroup *task_dfl_cgroup(struct task_struct *task)
+{
+	return task_css_set(task)->dfl_cgrp;
+}
+
+static inline struct cgroup *cgroup_parent(struct cgroup *cgrp)
+{
+	struct cgroup_subsys_state *parent_css = cgrp->self.parent;
+
+	if (parent_css)
+		return container_of(parent_css, struct cgroup, self);
+	return NULL;
+}
+
 /**
  * cgroup_is_descendant - test ancestry
  * @cgrp: the cgroup to be tested
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4b9a259bd413..11353701f40d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -358,15 +358,6 @@ static void cgroup_idr_remove(struct idr *idr, int id)
 	spin_unlock_bh(&cgroup_idr_lock);
 }
 
-static struct cgroup *cgroup_parent(struct cgroup *cgrp)
-{
-	struct cgroup_subsys_state *parent_css = cgrp->self.parent;
-
-	if (parent_css)
-		return container_of(parent_css, struct cgroup, self);
-	return NULL;
-}
-
 /* subsystems visibly enabled on a cgroup */
 static u16 cgroup_control(struct cgroup *cgrp)
 {
@@ -484,17 +475,6 @@ static inline bool cgroup_is_dead(const struct cgroup *cgrp)
 	return !(cgrp->self.flags & CSS_ONLINE);
 }
 
-static void cgroup_get(struct cgroup *cgrp)
-{
-	WARN_ON_ONCE(cgroup_is_dead(cgrp));
-	css_get(&cgrp->self);
-}
-
-static bool cgroup_tryget(struct cgroup *cgrp)
-{
-	return css_tryget(&cgrp->self);
-}
-
 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
 {
 	struct cgroup *cgrp = of->kn->parent->priv;