[PATCH] sched/group_sched: add task_group_is_root() api

[Hui Su <sh_def@163.com>]

Use task_group_is_root() instead of '!tg->se[0]'
and 'tg == &root_task_group' to judge whether a
task_group is root_task_group.

Signed-off-by: Hui Su <sh_def@163.com>
---
 kernel/sched/autogroup.c |  2 +-
 kernel/sched/core.c      | 11 ++++++++---
 kernel/sched/fair.c      |  4 ++--
 kernel/sched/rt.c        |  2 +-
 kernel/sched/sched.h     |  2 ++
 5 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/autogroup.c b/kernel/sched/autogroup.c
index 2067080bb235..2673ef7b50e2 100644
--- a/kernel/sched/autogroup.c
+++ b/kernel/sched/autogroup.c
@@ -106,7 +106,7 @@ static inline struct autogroup *autogroup_create(void)
 
 bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
 {
-	if (tg != &root_task_group)
+	if (!task_group_is_root(tg))
 		return false;
 	/*
 	 * If we race with autogroup_move_group() the caller can use the old
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d2003a7d5ab5..6002f9b67f07 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1075,7 +1075,7 @@ uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
 	 */
 	if (task_group_is_autogroup(task_group(p)))
 		return uc_req;
-	if (task_group(p) == &root_task_group)
+	if (task_group_is_root(task_group(p)))
 		return uc_req;
 
 	uc_max = task_group(p)->uclamp[clamp_id];
@@ -7574,6 +7574,11 @@ void sched_move_task(struct task_struct *tsk)
 	task_rq_unlock(rq, tsk, &rf);
 }
 
+bool task_group_is_root(struct task_group *tg)
+{
+	return tg == &root_task_group;
+}
+
 static inline struct task_group *css_tg(struct cgroup_subsys_state *css)
 {
 	return css ? container_of(css, struct task_group, css) : NULL;
@@ -7894,7 +7899,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
 	int i, ret = 0, runtime_enabled, runtime_was_enabled;
 	struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
 
-	if (tg == &root_task_group)
+	if (task_group_is_root(tg))
 		return -EINVAL;
 
 	/*
@@ -8138,7 +8143,7 @@ static int cpu_cfs_stat_show(struct seq_file *sf, void *v)
 	seq_printf(sf, "nr_throttled %d\n", cfs_b->nr_throttled);
 	seq_printf(sf, "throttled_time %llu\n", cfs_b->throttled_time);
 
-	if (schedstat_enabled() && tg != &root_task_group) {
+	if (schedstat_enabled() && !task_group_is_root(tg)) {
 		u64 ws = 0;
 		int i;
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 290f9e38378c..fa1a07d74e6a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3311,7 +3311,7 @@ static inline void update_tg_load_avg(struct cfs_rq *cfs_rq)
 	/*
 	 * No need to update load_avg for root_task_group as it is not used.
 	 */
-	if (cfs_rq->tg == &root_task_group)
+	if (task_group_is_root(cfs_rq->tg))
 		return;
 
 	if (abs(delta) > cfs_rq->tg_load_avg_contrib / 64) {
@@ -11095,7 +11095,7 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares)
 	/*
 	 * We can't change the weight of the root cgroup.
 	 */
-	if (!tg->se[0])
+	if (task_group_is_root(tg))
 		return -EINVAL;
 
 	shares = clamp(shares, scale_load(MIN_SHARES), scale_load(MAX_SHARES));
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 49ec096a8aa1..a7987564d5da 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2580,7 +2580,7 @@ static int tg_set_rt_bandwidth(struct task_group *tg,
 	 * Disallowing the root group RT runtime is BAD, it would disallow the
 	 * kernel creating (and or operating) RT threads.
 	 */
-	if (tg == &root_task_group && rt_runtime == 0)
+	if (task_group_is_root(tg) && rt_runtime == 0)
 		return -EINVAL;
 
 	/* No period doesn't make any sense. */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index df80bfcea92e..8758fbf0fa2a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -497,6 +497,8 @@ extern void sched_offline_group(struct task_group *tg);
 
 extern void sched_move_task(struct task_struct *tsk);
 
+extern bool task_group_is_root(struct task_group *tg);
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
 extern int sched_group_set_shares(struct task_group *tg, unsigned long shares);
 
-- 
2.25.1