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>
---
include/linux/sched.h | 5 ++---
kernel/sched/core.c | 30 +++++++-----------------------
kernel/sched/fair.c | 7 +++++++
3 files changed, 16 insertions(+), 26 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e7b2f8a5c711..0b296e855dee 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -96,10 +96,9 @@ struct task_group;
#define TASK_WAKEKILL 0x0100
#define TASK_WAKING 0x0200
#define TASK_NOLOAD 0x0400
-#define TASK_NEW 0x0800
/* RT specific auxilliary flag to mark RT lock waiters */
-#define TASK_RTLOCK_WAIT 0x1000
-#define TASK_STATE_MAX 0x2000
+#define TASK_RTLOCK_WAIT 0x0800
+#define TASK_STATE_MAX 0x1000
/* Convenience macros for the sake of set_current_state: */
#define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8e3f1c3f0b2c..157f7461a08a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4550,11 +4550,11 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
{
__sched_fork(clone_flags, p);
/*
- * We mark the process as NEW here. This guarantees that
+ * We mark the process as running here. This guarantees that
* nobody will actually run it, and a signal or other external
* event cannot wake it up and insert it on the runqueue either.
*/
- p->__state = TASK_NEW;
+ p->__state = TASK_RUNNING;
/*
* Make sure we do not leak PI boosting priority to the child.
@@ -4672,7 +4672,6 @@ void wake_up_new_task(struct task_struct *p)
struct rq *rq;
raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
- WRITE_ONCE(p->__state, TASK_RUNNING);
#ifdef CONFIG_SMP
/*
* Fork balancing, do it here and not earlier because:
@@ -10290,36 +10289,19 @@ 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)
{
@@ -11155,7 +11137,9 @@ 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 eba8a64f905a..e0d34ecdabae 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11840,6 +11840,13 @@ 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 (!p->on_rq && !p->se.sum_exec_runtime)
+ return;
+
detach_task_cfs_rq(p);
#ifdef CONFIG_SMP
--
2.37.2On Thu, Aug 18, 2022 at 11:43:41AM +0800, Chengming Zhou wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 8e3f1c3f0b2c..157f7461a08a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4550,11 +4550,11 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
> {
> __sched_fork(clone_flags, p);
> /*
> - * We mark the process as NEW here. This guarantees that
> + * We mark the process as running here. This guarantees that
> * nobody will actually run it, and a signal or other external
> * event cannot wake it up and insert it on the runqueue either.
> */
> - p->__state = TASK_NEW;
> + p->__state = TASK_RUNNING;
>
> /*
> * Make sure we do not leak PI boosting priority to the child.
> @@ -4672,7 +4672,6 @@ void wake_up_new_task(struct task_struct *p)
> struct rq *rq;
>
> raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
> - WRITE_ONCE(p->__state, TASK_RUNNING);
> #ifdef CONFIG_SMP
> /*
> * Fork balancing, do it here and not earlier because:
> @@ -10290,36 +10289,19 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
> sched_unregister_group(tg);
> }
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index eba8a64f905a..e0d34ecdabae 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -11840,6 +11840,13 @@ 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 (!p->on_rq && !p->se.sum_exec_runtime)
> + return;
> +
> detach_task_cfs_rq(p);
Wouldn't that be much clearer when expressed in TASK_NEW ?
On 2022/8/18 18:36, Peter Zijlstra wrote:
> On Thu, Aug 18, 2022 at 11:43:41AM +0800, Chengming Zhou wrote:
>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 8e3f1c3f0b2c..157f7461a08a 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -4550,11 +4550,11 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
>> {
>> __sched_fork(clone_flags, p);
>> /*
>> - * We mark the process as NEW here. This guarantees that
>> + * We mark the process as running here. This guarantees that
>> * nobody will actually run it, and a signal or other external
>> * event cannot wake it up and insert it on the runqueue either.
>> */
>> - p->__state = TASK_NEW;
>> + p->__state = TASK_RUNNING;
>>
>> /*
>> * Make sure we do not leak PI boosting priority to the child.
>> @@ -4672,7 +4672,6 @@ void wake_up_new_task(struct task_struct *p)
>> struct rq *rq;
>>
>> raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
>> - WRITE_ONCE(p->__state, TASK_RUNNING);
>> #ifdef CONFIG_SMP
>> /*
>> * Fork balancing, do it here and not earlier because:
>> @@ -10290,36 +10289,19 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
>> sched_unregister_group(tg);
>> }
>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index eba8a64f905a..e0d34ecdabae 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -11840,6 +11840,13 @@ 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 (!p->on_rq && !p->se.sum_exec_runtime)
>> + return;
>> +
>> detach_task_cfs_rq(p);
>
> Wouldn't that be much clearer when expressed in TASK_NEW ?
Ah, I was stupid, will change to use TASK_NEW.
Thanks for your suggestion!
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