[PATCH v4 2/9] sched/fair: remove redundant cpu_cgrp_subsys->fork()

From: Chengming Zhou
Date: Mon Aug 08 2022 - 08:58:22 EST


We use cpu_cgrp_subsys->fork() to set task group for the new fair task
in cgroup_post_fork().

Since commit b1e8206582f9 ("sched: Fix yet more sched_fork() races")
has already set_task_rq() for the new fair task in sched_cgroup_fork(),
so cpu_cgrp_subsys->fork() can be removed.

cgroup_can_fork() --> pin parent's sched_task_group
sched_cgroup_fork()
__set_task_cpu()
set_task_rq()
cgroup_post_fork()
ss->fork() := cpu_cgroup_fork()
sched_change_group(..., TASK_SET_GROUP)
task_set_group_fair()
set_task_rq() --> can be removed

After this patch's change, task_change_group_fair() only need to
care about task cgroup migration, make the code much simplier.

Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
---
kernel/sched/core.c | 27 ++++-----------------------
kernel/sched/fair.c | 23 +----------------------
kernel/sched/sched.h | 5 +----
3 files changed, 6 insertions(+), 49 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 64c08993221b..e74e79f783af 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -481,8 +481,7 @@ sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags) { }
* p->se.load, p->rt_priority,
* p->dl.dl_{runtime, deadline, period, flags, bw, density}
* - sched_setnuma(): p->numa_preferred_nid
- * - sched_move_task()/
- * cpu_cgroup_fork(): p->sched_task_group
+ * - sched_move_task(): p->sched_task_group
* - uclamp_update_active() p->uclamp*
*
* p->state <- TASK_*:
@@ -10114,7 +10113,7 @@ void sched_release_group(struct task_group *tg)
spin_unlock_irqrestore(&task_group_lock, flags);
}

-static void sched_change_group(struct task_struct *tsk, int type)
+static void sched_change_group(struct task_struct *tsk)
{
struct task_group *tg;

@@ -10130,7 +10129,7 @@ static void sched_change_group(struct task_struct *tsk, int type)

#ifdef CONFIG_FAIR_GROUP_SCHED
if (tsk->sched_class->task_change_group)
- tsk->sched_class->task_change_group(tsk, type);
+ tsk->sched_class->task_change_group(tsk);
else
#endif
set_task_rq(tsk, task_cpu(tsk));
@@ -10161,7 +10160,7 @@ void sched_move_task(struct task_struct *tsk)
if (running)
put_prev_task(rq, tsk);

- sched_change_group(tsk, TASK_MOVE_GROUP);
+ sched_change_group(tsk);

if (queued)
enqueue_task(rq, tsk, queue_flags);
@@ -10239,23 +10238,6 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
sched_unregister_group(tg);
}

-/*
- * This is called before wake_up_new_task(), therefore we really only
- * have to set its group bits, all the other stuff does not apply.
- */
-static void cpu_cgroup_fork(struct task_struct *task)
-{
- struct rq_flags rf;
- struct rq *rq;
-
- rq = task_rq_lock(task, &rf);
-
- update_rq_clock(rq);
- sched_change_group(task, TASK_SET_GROUP);
-
- task_rq_unlock(rq, task, &rf);
-}
-
static int cpu_cgroup_can_attach(struct cgroup_taskset *tset)
{
struct task_struct *task;
@@ -11121,7 +11103,6 @@ struct cgroup_subsys cpu_cgrp_subsys = {
.css_released = cpu_cgroup_css_released,
.css_free = cpu_cgroup_css_free,
.css_extra_stat_show = cpu_extra_stat_show,
- .fork = cpu_cgroup_fork,
.can_attach = cpu_cgroup_can_attach,
.attach = cpu_cgroup_attach,
.legacy_cftypes = cpu_legacy_files,
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a3b0f8b1029e..2c0eb2a4e341 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11657,15 +11657,7 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
}

#ifdef CONFIG_FAIR_GROUP_SCHED
-static void task_set_group_fair(struct task_struct *p)
-{
- struct sched_entity *se = &p->se;
-
- set_task_rq(p, task_cpu(p));
- se->depth = se->parent ? se->parent->depth + 1 : 0;
-}
-
-static void task_move_group_fair(struct task_struct *p)
+static void task_change_group_fair(struct task_struct *p)
{
detach_task_cfs_rq(p);
set_task_rq(p, task_cpu(p));
@@ -11677,19 +11669,6 @@ static void task_move_group_fair(struct task_struct *p)
attach_task_cfs_rq(p);
}

-static void task_change_group_fair(struct task_struct *p, int type)
-{
- switch (type) {
- case TASK_SET_GROUP:
- task_set_group_fair(p);
- break;
-
- case TASK_MOVE_GROUP:
- task_move_group_fair(p);
- break;
- }
-}
-
void free_fair_sched_group(struct task_group *tg)
{
int i;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 4c4822141026..74130a69d365 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2193,11 +2193,8 @@ struct sched_class {

void (*update_curr)(struct rq *rq);

-#define TASK_SET_GROUP 0
-#define TASK_MOVE_GROUP 1
-
#ifdef CONFIG_FAIR_GROUP_SCHED
- void (*task_change_group)(struct task_struct *p, int type);
+ void (*task_change_group)(struct task_struct *p);
#endif
};

--
2.36.1