sched/fair: Allow changing cgroup of new forked task

commit 7dc603c9028e ("sched/fair: Fix PELT integrity for new tasks")
introduce a TASK_NEW state and an unnessary limitation that would fail
when changing cgroup of new forked task.

Because at that time, we can't handle task_change_group_fair() for new
forked fair task which hasn't been woken up by wake_up_new_task(),
which will cause detach on an unattached task sched_avg problem.

This patch delete this unnessary limitation by adding check before do
detach or attach in task_change_group_fair().

So cpu_cgrp_subsys.can_attach() has nothing to do for fair tasks,
only define it in #ifdef CONFIG_RT_GROUP_SCHED.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20220818124805.601-8-zhouchengming@bytedance.com

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e74e79f783afad27ef09774a5f80c90cc10ea6c1..603a80ec9b0eb77fa5de34107b16333451000345 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10238,36 +10238,19 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
        sched_unregister_group(tg);
 }
 
+#ifdef CONFIG_RT_GROUP_SCHED
 static int cpu_cgroup_can_attach(struct cgroup_taskset *tset)
 {
        struct task_struct *task;
        struct cgroup_subsys_state *css;
-       int ret = 0;
 
        cgroup_taskset_for_each(task, css, tset) {
-#ifdef CONFIG_RT_GROUP_SCHED
                if (!sched_rt_can_attach(css_tg(css), task))
                        return -EINVAL;
-#endif
-               /*
-                * Serialize against wake_up_new_task() such that if it's
-                * running, we're sure to observe its full state.
-                */
-               raw_spin_lock_irq(&task->pi_lock);
-               /*
-                * Avoid calling sched_move_task() before wake_up_new_task()
-                * has happened. This would lead to problems with PELT, due to
-                * move wanting to detach+attach while we're not attached yet.
-                */
-               if (READ_ONCE(task->__state) == TASK_NEW)
-                       ret = -EINVAL;
-               raw_spin_unlock_irq(&task->pi_lock);
-
-               if (ret)
-                       break;
        }
-       return ret;
+       return 0;
 }
+#endif
 
 static void cpu_cgroup_attach(struct cgroup_taskset *tset)
 {
@@ -11103,7 +11086,9 @@ 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,
+#ifdef CONFIG_RT_GROUP_SCHED
        .can_attach     = cpu_cgroup_can_attach,
+#endif
        .attach         = cpu_cgroup_attach,
        .legacy_cftypes = cpu_legacy_files,
        .dfl_cftypes    = cpu_files,

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e92bc053aff6004a3d99d55eb1f5414cb22e59ab..fd1aa4c92b2dbed4399cce58cebe4cf8245c5422 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11676,6 +11676,13 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static void task_change_group_fair(struct task_struct *p)
 {
+       /*
+        * We couldn't detach or attach a forked task which
+        * hasn't been woken up by wake_up_new_task().
+        */
+       if (READ_ONCE(p->__state) == TASK_NEW)
+               return;
+
        detach_task_cfs_rq(p);
 
 #ifdef CONFIG_SMP