[PATCH v5 0/4] Fix some warnings about rq clock

[PATCH v5 0/4] Fix some warnings about rq clock

[Hao Jia]

These four patches fix some warnings about rq clock.

Patch1 fixes the warning of using the old rq clock caused by
missing update rq clock.

Patch2-4 fixes the warning that the rq clock was updated multiple
times while holding the rq lock.

v4->v5:
    - Benjamin Segall suggested adding update_rq_clock() to set_rq_offline()
      instead of calling update_rq_clock() before set_rq_offline() runs.

v3->v4:
    - Add Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> for
      all patches.

v2->v3:
    - Modify the commit information of patch1 to make the description clearer.
    - Split v2 patch2 into 3 separate patches.

v1->v2:
    - Vincent Guittot suggested using rq_clock_start_loop_update()
      to prevent multiple calls to update_rq_clock() in unthrottle_cfs_rq()
      instead of removing update_rq_clock() from unthrottle_cfs_rq()
      and updating the rq clock before unthrottle_cfs_rq() for patch2.

[v4] https://lore.kernel.org/all/20230608063312.79440-1-jiahao.os@bytedance.com
[v3] https://lore.kernel.org/all/20230515063848.77947-1-jiahao.os@bytedance.com
[v2] https://lore.kernel.org/all/20230510083450.62334-1-jiahao.os@bytedance.com
[v1] https://lore.kernel.org/all/20230410081206.23441-1-jiahao.os@bytedance.com


Hao Jia (4):
  sched/core: Fixed missing rq clock update before calling
    set_rq_offline()
  sched/core: Avoid double calling update_rq_clock() in
    __balance_push_cpu_stop()
  sched/core: Avoid multiple calling update_rq_clock() in
    __cfsb_csd_unthrottle()
  sched/core: Avoid multiple calling update_rq_clock() in
    unthrottle_offline_cfs_rqs()

 kernel/sched/core.c     |  9 +++++----
 kernel/sched/fair.c     | 18 ++++++++++++++++++
 kernel/sched/sched.h    | 21 +++++++++++++++++++++
 kernel/sched/topology.c |  6 +++---
 4 files changed, 47 insertions(+), 7 deletions(-)

-- 
2.20.1

[PATCH v5 1/4] sched/core: Fixed missing rq clock update before calling set_rq_offline()

[Hao Jia]

This is triggered during cpu offline when CONFIG_CPU_FREQ is enabled
and cpufreq is set to powersave:
------------[ cut here ]------------
rq->clock_update_flags < RQCF_ACT_SKIP
WARNING: CPU: 24 PID: 754 at kernel/sched/sched.h:1496
enqueue_top_rt_rq+0x139/0x160
Call Trace:
 <TASK>
 ? intel_pstate_update_util+0x3b0/0x3b0
 rq_offline_rt+0x1b7/0x250
 set_rq_offline.part.120+0x28/0x60
 rq_attach_root+0xc4/0xd0
 cpu_attach_domain+0x3dc/0x7f0
 ? __schedule+0x65e/0x1310
 partition_sched_domains_locked+0x2a5/0x3c0
 rebuild_sched_domains_locked+0x477/0x830
 ? percpu_rwsem_wait+0x140/0x140
 rebuild_sched_domains+0x1b/0x30
 cpuset_hotplug_workfn+0x2ca/0xc90
 ? balance_push+0x56/0x120
 ? _raw_spin_unlock+0x15/0x30
 ? finish_task_switch+0x98/0x2f0
 ? __switch_to+0x116/0x410
 ? __schedule+0x65e/0x1310 ? internal_add_timer+0x42/0x60
 ? _raw_spin_unlock_irqrestore+0x23/0x40
 ? add_timer_on+0xd5/0x130
 process_one_work+0x1bc/0x3d0
 worker_thread+0x4c/0x380
 ? preempt_count_add+0x56/0xa0
 ? rescuer_thread+0x310/0x310
 kthread+0xe6/0x110
 ? kthread_complete_and_exit+0x20/0x20
 ret_from_fork+0x1f/0x30

More detailed key function call graph:
rq_offline_rt()
  __disable_runtime()
    sched_rt_rq_enqueue()
      enqueue_top_rt_rq()
        cpufreq_update_util() <-- depends on CONFIG_CPU_FREQ
          data->func(data, *rq_clock(rq)*, flags)
            intel_pstate_update_util() <-- powersave policy callback function

Before calling rq_offline_rt() we need to update the rq clock to avoid
using the old rq clock, So we add update_rq_clock() to set_rq_offline()
to update rq clock. And we use rq_lock_irqsave()/rq_unlock_irqrestore()
to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore()
in rq_attach_root() to ensure that rq->clock_update_flags are cleared
before updating the rq clock.

Steps to reproduce:
1. Enable CONFIG_SMP and CONFIG_CPU_FREQ when compiling the kernel
2. echo 1 > /sys/kernel/debug/clear_warn_once
3. cpupower -c all frequency-set -g powersave
4. Run some rt tasks e.g. Create 5*n rt (100% running) tasks (on a
   system with n CPUs)
5. Offline cpu one by one until the warninng is triggered

Suggested-by: Ben Segall <bsegall@google.com>
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
---
 kernel/sched/core.c     | 2 +-
 kernel/sched/topology.c | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a68d1276bab0..a8be5415daba 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9548,6 +9548,7 @@ void set_rq_offline(struct rq *rq)
 	if (rq->online) {
 		const struct sched_class *class;
 
+		update_rq_clock(rq);
 		for_each_class(class) {
 			if (class->rq_offline)
 				class->rq_offline(rq);
@@ -9689,7 +9690,6 @@ int sched_cpu_deactivate(unsigned int cpu)
 
 	rq_lock_irqsave(rq, &rf);
 	if (rq->rd) {
-		update_rq_clock(rq);
 		BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
 		set_rq_offline(rq);
 	}
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 6682535e37c8..52976eadfee9 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -487,9 +487,9 @@ static void free_rootdomain(struct rcu_head *rcu)
 void rq_attach_root(struct rq *rq, struct root_domain *rd)
 {
 	struct root_domain *old_rd = NULL;
-	unsigned long flags;
+	struct rq_flags rf;
 
-	raw_spin_rq_lock_irqsave(rq, flags);
+	rq_lock_irqsave(rq, &rf);
 
 	if (rq->rd) {
 		old_rd = rq->rd;
@@ -515,7 +515,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
 	if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
 		set_rq_online(rq);
 
-	raw_spin_rq_unlock_irqrestore(rq, flags);
+	rq_unlock_irqrestore(rq, &rf);
 
 	if (old_rd)
 		call_rcu(&old_rd->rcu, free_rootdomain);
-- 
2.20.1

[PATCH v5 2/4] sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()

[Hao Jia]

The WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
------------[ cut here ]------------
rq->clock_update_flags & RQCF_UPDATED
WARNING: CPU: 17 PID: 138 at kernel/sched/core.c:741
update_rq_clock+0xaf/0x180
Call Trace:
 <TASK>
 __balance_push_cpu_stop+0x146/0x180
 ? migration_cpu_stop+0x2a0/0x2a0
 cpu_stopper_thread+0xa3/0x140
 smpboot_thread_fn+0x14f/0x210
 ? sort_range+0x20/0x20
 kthread+0xe6/0x110
 ? kthread_complete_and_exit+0x20/0x20
 ret_from_fork+0x1f/0x30

To avoid this warning, we remove update_rq_clock() from
the __migrate_task() function. And in order to avoid
missing rq clock update, add update_rq_clock() call before
migration_cpu_stop() calls __migrate_task().

Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a8be5415daba..1eca36299d8b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2398,7 +2398,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
 	if (!is_cpu_allowed(p, dest_cpu))
 		return rq;
 
-	update_rq_clock(rq);
 	rq = move_queued_task(rq, rf, p, dest_cpu);
 
 	return rq;
@@ -2456,10 +2455,12 @@ static int migration_cpu_stop(void *data)
 				goto out;
 		}
 
-		if (task_on_rq_queued(p))
+		if (task_on_rq_queued(p)) {
+			update_rq_clock(rq);
 			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
-		else
+		} else {
 			p->wake_cpu = arg->dest_cpu;
+		}
 
 		/*
 		 * XXX __migrate_task() can fail, at which point we might end
-- 
2.20.1

[PATCH v5 3/4] sched/core: Avoid multiple calling update_rq_clock() in __cfsb_csd_unthrottle()

[Hao Jia]

After commit 8ad075c2eb1f ("sched: Async unthrottling for cfs
bandwidth"), we may update the rq clock multiple times in the loop of
__cfsb_csd_unthrottle(). At that time the following warning will be
triggered.
------------[ cut here ]------------
rq->clock_update_flags & RQCF_UPDATED
WARNING: CPU: 54 PID: 0 at kernel/sched/core.c:741
update_rq_clock+0xaf/0x180
Call Trace:
 <TASK>
 unthrottle_cfs_rq+0x4b/0x300
 __cfsb_csd_unthrottle+0xe0/0x100
 __flush_smp_call_function_queue+0xaf/0x1d0
 flush_smp_call_function_queue+0x49/0x90
 do_idle+0x17c/0x270
 cpu_startup_entry+0x19/0x20
 start_secondary+0xfa/0x120
 secondary_startup_64_no_verify+0xce/0xdb

Before the loop starts, we update the rq clock once and call
rq_clock_start_loop_update() to prevent updating the rq clock
multiple times. And call rq_clock_stop_loop_update() After
the loop to clear rq->clock_update_flags.

Fixes: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")

Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/fair.c  |  9 +++++++++
 kernel/sched/sched.h | 21 +++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 373ff5f55884..af9604f4b135 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5576,6 +5576,14 @@ static void __cfsb_csd_unthrottle(void *arg)
 
 	rq_lock(rq, &rf);
 
+	/*
+	 * Iterating over the list can trigger several call to
+	 * update_rq_clock() in unthrottle_cfs_rq().
+	 * Do it once and skip the potential next ones.
+	 */
+	update_rq_clock(rq);
+	rq_clock_start_loop_update(rq);
+
 	/*
 	 * Since we hold rq lock we're safe from concurrent manipulation of
 	 * the CSD list. However, this RCU critical section annotates the
@@ -5595,6 +5603,7 @@ static void __cfsb_csd_unthrottle(void *arg)
 
 	rcu_read_unlock();
 
+	rq_clock_stop_loop_update(rq);
 	rq_unlock(rq, &rf);
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ec7b3e0a2b20..50446e401b9f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1546,6 +1546,27 @@ static inline void rq_clock_cancel_skipupdate(struct rq *rq)
 	rq->clock_update_flags &= ~RQCF_REQ_SKIP;
 }
 
+/*
+ * During cpu offlining and rq wide unthrottling, we can trigger
+ * an update_rq_clock() for several cfs and rt runqueues (Typically
+ * when using list_for_each_entry_*)
+ * rq_clock_start_loop_update() can be called after updating the clock
+ * once and before iterating over the list to prevent multiple update.
+ * After the iterative traversal, we need to call rq_clock_stop_loop_update()
+ * to clear RQCF_ACT_SKIP of rq->clock_update_flags.
+ */
+static inline void rq_clock_start_loop_update(struct rq *rq)
+{
+	lockdep_assert_rq_held(rq);
+	rq->clock_update_flags |= RQCF_ACT_SKIP;
+}
+
+static inline void rq_clock_stop_loop_update(struct rq *rq)
+{
+	lockdep_assert_rq_held(rq);
+	rq->clock_update_flags &= ~RQCF_ACT_SKIP;
+}
+
 struct rq_flags {
 	unsigned long flags;
 	struct pin_cookie cookie;
-- 
2.20.1

[PATCH v5 4/4] sched/core: Avoid multiple calling update_rq_clock() in unthrottle_offline_cfs_rqs()

[Hao Jia]

This WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
------------[ cut here ]------------
rq->clock_update_flags & RQCF_UPDATED
WARNING: CPU: 0 PID: 3323 at kernel/sched/core.c:741
update_rq_clock+0xaf/0x180
Call Trace:
 <TASK>
 unthrottle_cfs_rq+0x4b/0x300
 rq_offline_fair+0x89/0x90
 set_rq_offline.part.118+0x28/0x60
 rq_attach_root+0xc4/0xd0
 cpu_attach_domain+0x3dc/0x7f0
 partition_sched_domains_locked+0x2a5/0x3c0
 rebuild_sched_domains_locked+0x477/0x830
 rebuild_sched_domains+0x1b/0x30
 cpuset_hotplug_workfn+0x2ca/0xc90
 ? balance_push+0x56/0xf0
 ? _raw_spin_unlock+0x15/0x30
 ? finish_task_switch+0x98/0x2f0
 ? __switch_to+0x291/0x410
 ? __schedule+0x65e/0x1310
 process_one_work+0x1bc/0x3d0
 worker_thread+0x4c/0x380
 ? preempt_count_add+0x92/0xa0
 ? rescuer_thread+0x310/0x310
 kthread+0xe6/0x110
 ? kthread_complete_and_exit+0x20/0x20
 ret_from_fork+0x1f/0x30

The rq clock has been updated in the set_rq_offline(),
so we don't need to call update_rq_clock() in
unthrottle_offline_cfs_rqs().
We only need to call rq_clock_start_loop_update() before the
loop starts and rq_clock_stop_loop_update() after the loop
to avoid this warning.

Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/fair.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index af9604f4b135..4da5f3541762 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6124,6 +6124,13 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
 
 	lockdep_assert_rq_held(rq);
 
+	/*
+	 * The rq clock has already been updated in the
+	 * set_rq_offline(), so we should skip updating
+	 * the rq clock again in unthrottle_cfs_rq().
+	 */
+	rq_clock_start_loop_update(rq);
+
 	rcu_read_lock();
 	list_for_each_entry_rcu(tg, &task_groups, list) {
 		struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
@@ -6146,6 +6153,8 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
 			unthrottle_cfs_rq(cfs_rq);
 	}
 	rcu_read_unlock();
+
+	rq_clock_stop_loop_update(rq);
 }
 
 #else /* CONFIG_CFS_BANDWIDTH */
-- 
2.20.1

Re: [PATCH v5 1/4] sched/core: Fixed missing rq clock update before calling set_rq_offline()

[Hao Jia]

On 2023/6/13 Hao Jia wrote:
> This is triggered during cpu offline when CONFIG_CPU_FREQ is enabled
> and cpufreq is set to powersave:
> ------------[ cut here ]------------
> rq->clock_update_flags < RQCF_ACT_SKIP
> WARNING: CPU: 24 PID: 754 at kernel/sched/sched.h:1496
> enqueue_top_rt_rq+0x139/0x160
> Call Trace:
>   <TASK>
>   ? intel_pstate_update_util+0x3b0/0x3b0
>   rq_offline_rt+0x1b7/0x250
>   set_rq_offline.part.120+0x28/0x60
>   rq_attach_root+0xc4/0xd0
>   cpu_attach_domain+0x3dc/0x7f0
>   ? __schedule+0x65e/0x1310
>   partition_sched_domains_locked+0x2a5/0x3c0
>   rebuild_sched_domains_locked+0x477/0x830
>   ? percpu_rwsem_wait+0x140/0x140
>   rebuild_sched_domains+0x1b/0x30
>   cpuset_hotplug_workfn+0x2ca/0xc90
>   ? balance_push+0x56/0x120
>   ? _raw_spin_unlock+0x15/0x30
>   ? finish_task_switch+0x98/0x2f0
>   ? __switch_to+0x116/0x410
>   ? __schedule+0x65e/0x1310 ? internal_add_timer+0x42/0x60
>   ? _raw_spin_unlock_irqrestore+0x23/0x40
>   ? add_timer_on+0xd5/0x130
>   process_one_work+0x1bc/0x3d0
>   worker_thread+0x4c/0x380
>   ? preempt_count_add+0x56/0xa0
>   ? rescuer_thread+0x310/0x310
>   kthread+0xe6/0x110
>   ? kthread_complete_and_exit+0x20/0x20
>   ret_from_fork+0x1f/0x30
> 
> More detailed key function call graph:
> rq_offline_rt()
>    __disable_runtime()
>      sched_rt_rq_enqueue()
>        enqueue_top_rt_rq()
>          cpufreq_update_util() <-- depends on CONFIG_CPU_FREQ
>            data->func(data, *rq_clock(rq)*, flags)
>              intel_pstate_update_util() <-- powersave policy callback function
> 
> Before calling rq_offline_rt() we need to update the rq clock to avoid
> using the old rq clock, So we add update_rq_clock() to set_rq_offline()
> to update rq clock. And we use rq_lock_irqsave()/rq_unlock_irqrestore()
> to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore()
> in rq_attach_root() to ensure that rq->clock_update_flags are cleared
> before updating the rq clock.
> 
> Steps to reproduce:
> 1. Enable CONFIG_SMP and CONFIG_CPU_FREQ when compiling the kernel
> 2. echo 1 > /sys/kernel/debug/clear_warn_once
> 3. cpupower -c all frequency-set -g powersave
> 4. Run some rt tasks e.g. Create 5*n rt (100% running) tasks (on a
>     system with n CPUs)
> 5. Offline cpu one by one until the warninng is triggered
> 
> Suggested-by: Ben Segall <bsegall@google.com>
> Signed-off-by: Hao Jia <jiahao.os@bytedance.com>

Hi Vincent,

   Benjamin Segall suggested adding update_rq_clock() to set_rq_offline()
instead of calling update_rq_clock() before set_rq_offline() runs.
The code of patch1 has changed, so I removed your tag "Reviewed-by". 
Please review again.

Thanks,
Hao

> ---
>   kernel/sched/core.c     | 2 +-
>   kernel/sched/topology.c | 6 +++---
>   2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a68d1276bab0..a8be5415daba 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9548,6 +9548,7 @@ void set_rq_offline(struct rq *rq)
>   	if (rq->online) {
>   		const struct sched_class *class;
>   
> +		update_rq_clock(rq);
>   		for_each_class(class) {
>   			if (class->rq_offline)
>   				class->rq_offline(rq);
> @@ -9689,7 +9690,6 @@ int sched_cpu_deactivate(unsigned int cpu)
>   
>   	rq_lock_irqsave(rq, &rf);
>   	if (rq->rd) {
> -		update_rq_clock(rq);
>   		BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
>   		set_rq_offline(rq);
>   	}
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 6682535e37c8..52976eadfee9 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -487,9 +487,9 @@ static void free_rootdomain(struct rcu_head *rcu)
>   void rq_attach_root(struct rq *rq, struct root_domain *rd)
>   {
>   	struct root_domain *old_rd = NULL;
> -	unsigned long flags;
> +	struct rq_flags rf;
>   
> -	raw_spin_rq_lock_irqsave(rq, flags);
> +	rq_lock_irqsave(rq, &rf);
>   
>   	if (rq->rd) {
>   		old_rd = rq->rd;
> @@ -515,7 +515,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
>   	if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
>   		set_rq_online(rq);
>   
> -	raw_spin_rq_unlock_irqrestore(rq, flags);
> +	rq_unlock_irqrestore(rq, &rf);
>   
>   	if (old_rd)
>   		call_rcu(&old_rd->rcu, free_rootdomain);

Re: [PATCH v5 1/4] sched/core: Fixed missing rq clock update before calling set_rq_offline()

[Vincent Guittot]

On Tue, 13 Jun 2023 at 10:31, Hao Jia <jiahao.os@bytedance.com> wrote:
>
>
>
> On 2023/6/13 Hao Jia wrote:
> > This is triggered during cpu offline when CONFIG_CPU_FREQ is enabled
> > and cpufreq is set to powersave:
> > ------------[ cut here ]------------
> > rq->clock_update_flags < RQCF_ACT_SKIP
> > WARNING: CPU: 24 PID: 754 at kernel/sched/sched.h:1496
> > enqueue_top_rt_rq+0x139/0x160
> > Call Trace:
> >   <TASK>
> >   ? intel_pstate_update_util+0x3b0/0x3b0
> >   rq_offline_rt+0x1b7/0x250
> >   set_rq_offline.part.120+0x28/0x60
> >   rq_attach_root+0xc4/0xd0
> >   cpu_attach_domain+0x3dc/0x7f0
> >   ? __schedule+0x65e/0x1310
> >   partition_sched_domains_locked+0x2a5/0x3c0
> >   rebuild_sched_domains_locked+0x477/0x830
> >   ? percpu_rwsem_wait+0x140/0x140
> >   rebuild_sched_domains+0x1b/0x30
> >   cpuset_hotplug_workfn+0x2ca/0xc90
> >   ? balance_push+0x56/0x120
> >   ? _raw_spin_unlock+0x15/0x30
> >   ? finish_task_switch+0x98/0x2f0
> >   ? __switch_to+0x116/0x410
> >   ? __schedule+0x65e/0x1310 ? internal_add_timer+0x42/0x60
> >   ? _raw_spin_unlock_irqrestore+0x23/0x40
> >   ? add_timer_on+0xd5/0x130
> >   process_one_work+0x1bc/0x3d0
> >   worker_thread+0x4c/0x380
> >   ? preempt_count_add+0x56/0xa0
> >   ? rescuer_thread+0x310/0x310
> >   kthread+0xe6/0x110
> >   ? kthread_complete_and_exit+0x20/0x20
> >   ret_from_fork+0x1f/0x30
> >
> > More detailed key function call graph:
> > rq_offline_rt()
> >    __disable_runtime()
> >      sched_rt_rq_enqueue()
> >        enqueue_top_rt_rq()
> >          cpufreq_update_util() <-- depends on CONFIG_CPU_FREQ
> >            data->func(data, *rq_clock(rq)*, flags)
> >              intel_pstate_update_util() <-- powersave policy callback function
> >
> > Before calling rq_offline_rt() we need to update the rq clock to avoid
> > using the old rq clock, So we add update_rq_clock() to set_rq_offline()
> > to update rq clock. And we use rq_lock_irqsave()/rq_unlock_irqrestore()
> > to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore()
> > in rq_attach_root() to ensure that rq->clock_update_flags are cleared
> > before updating the rq clock.
> >
> > Steps to reproduce:
> > 1. Enable CONFIG_SMP and CONFIG_CPU_FREQ when compiling the kernel
> > 2. echo 1 > /sys/kernel/debug/clear_warn_once
> > 3. cpupower -c all frequency-set -g powersave
> > 4. Run some rt tasks e.g. Create 5*n rt (100% running) tasks (on a
> >     system with n CPUs)
> > 5. Offline cpu one by one until the warninng is triggered
> >
> > Suggested-by: Ben Segall <bsegall@google.com>
> > Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
>
> Hi Vincent,
>
>    Benjamin Segall suggested adding update_rq_clock() to set_rq_offline()
> instead of calling update_rq_clock() before set_rq_offline() runs.
> The code of patch1 has changed, so I removed your tag "Reviewed-by".
> Please review again.

v5 looks good to me

Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>

>
> Thanks,
> Hao
>
> > ---
> >   kernel/sched/core.c     | 2 +-
> >   kernel/sched/topology.c | 6 +++---
> >   2 files changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index a68d1276bab0..a8be5415daba 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -9548,6 +9548,7 @@ void set_rq_offline(struct rq *rq)
> >       if (rq->online) {
> >               const struct sched_class *class;
> >
> > +             update_rq_clock(rq);
> >               for_each_class(class) {
> >                       if (class->rq_offline)
> >                               class->rq_offline(rq);
> > @@ -9689,7 +9690,6 @@ int sched_cpu_deactivate(unsigned int cpu)
> >
> >       rq_lock_irqsave(rq, &rf);
> >       if (rq->rd) {
> > -             update_rq_clock(rq);
> >               BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
> >               set_rq_offline(rq);
> >       }
> > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> > index 6682535e37c8..52976eadfee9 100644
> > --- a/kernel/sched/topology.c
> > +++ b/kernel/sched/topology.c
> > @@ -487,9 +487,9 @@ static void free_rootdomain(struct rcu_head *rcu)
> >   void rq_attach_root(struct rq *rq, struct root_domain *rd)
> >   {
> >       struct root_domain *old_rd = NULL;
> > -     unsigned long flags;
> > +     struct rq_flags rf;
> >
> > -     raw_spin_rq_lock_irqsave(rq, flags);
> > +     rq_lock_irqsave(rq, &rf);
> >
> >       if (rq->rd) {
> >               old_rd = rq->rd;
> > @@ -515,7 +515,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
> >       if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
> >               set_rq_online(rq);
> >
> > -     raw_spin_rq_unlock_irqrestore(rq, flags);
> > +     rq_unlock_irqrestore(rq, &rf);
> >
> >       if (old_rd)
> >               call_rcu(&old_rd->rcu, free_rootdomain);

Re: [PATCH v5 4/4] sched/core: Avoid multiple calling update_rq_clock() in unthrottle_offline_cfs_rqs()

[Benjamin Segall]

Hao Jia <jiahao.os@bytedance.com> writes:

> This WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
> ------------[ cut here ]------------
> rq->clock_update_flags & RQCF_UPDATED
> WARNING: CPU: 0 PID: 3323 at kernel/sched/core.c:741
> update_rq_clock+0xaf/0x180
> Call Trace:
>  <TASK>
>  unthrottle_cfs_rq+0x4b/0x300
>  rq_offline_fair+0x89/0x90
>  set_rq_offline.part.118+0x28/0x60
>  rq_attach_root+0xc4/0xd0
>  cpu_attach_domain+0x3dc/0x7f0
>  partition_sched_domains_locked+0x2a5/0x3c0
>  rebuild_sched_domains_locked+0x477/0x830
>  rebuild_sched_domains+0x1b/0x30
>  cpuset_hotplug_workfn+0x2ca/0xc90
>  ? balance_push+0x56/0xf0
>  ? _raw_spin_unlock+0x15/0x30
>  ? finish_task_switch+0x98/0x2f0
>  ? __switch_to+0x291/0x410
>  ? __schedule+0x65e/0x1310
>  process_one_work+0x1bc/0x3d0
>  worker_thread+0x4c/0x380
>  ? preempt_count_add+0x92/0xa0
>  ? rescuer_thread+0x310/0x310
>  kthread+0xe6/0x110
>  ? kthread_complete_and_exit+0x20/0x20
>  ret_from_fork+0x1f/0x30
>
> The rq clock has been updated in the set_rq_offline(),
> so we don't need to call update_rq_clock() in
> unthrottle_offline_cfs_rqs().
> We only need to call rq_clock_start_loop_update() before the
> loop starts and rq_clock_stop_loop_update() after the loop
> to avoid this warning.
>

Both of these cfsb patches look sensible to me.

Reviewed-By: Ben Segall <bsegall@google.com>

Re: [PATCH v5 2/4] sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()

[Peter Zijlstra]

On Tue, Jun 13, 2023 at 04:20:10PM +0800, Hao Jia wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a8be5415daba..1eca36299d8b 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2398,7 +2398,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
>  	if (!is_cpu_allowed(p, dest_cpu))
>  		return rq;
>  
> -	update_rq_clock(rq);
>  	rq = move_queued_task(rq, rf, p, dest_cpu);
>  
>  	return rq;
> @@ -2456,10 +2455,12 @@ static int migration_cpu_stop(void *data)
>  				goto out;
>  		}
>  
> -		if (task_on_rq_queued(p))
> +		if (task_on_rq_queued(p)) {
> +			update_rq_clock(rq);
>  			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
> -		else
> +		} else {
>  			p->wake_cpu = arg->dest_cpu;
> +		}
>  
>  		/*
>  		 * XXX __migrate_task() can fail, at which point we might end

So now you've got update_rq_clock() in both callers, why not remove it
from __balance_push_cpu_stop() ?

Afaict nothing actually needs it before __migrate_task().

---
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9435,8 +9435,6 @@ static int __balance_push_cpu_stop(void
 	raw_spin_lock_irq(&p->pi_lock);
 	rq_lock(rq, &rf);
 
-	update_rq_clock(rq);
-
 	if (task_rq(p) == rq && task_on_rq_queued(p)) {
 		cpu = select_fallback_rq(rq->cpu, p);
 		rq = __migrate_task(rq, &rf, p, cpu);

Re: [External] Re: [PATCH v5 2/4] sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()

[Hao Jia]

On 2023/6/15 Peter Zijlstra wrote:
> On Tue, Jun 13, 2023 at 04:20:10PM +0800, Hao Jia wrote:
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index a8be5415daba..1eca36299d8b 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -2398,7 +2398,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
>>   	if (!is_cpu_allowed(p, dest_cpu))
>>   		return rq;
>>   
>> -	update_rq_clock(rq);
>>   	rq = move_queued_task(rq, rf, p, dest_cpu);
>>   
>>   	return rq;
>> @@ -2456,10 +2455,12 @@ static int migration_cpu_stop(void *data)
>>   				goto out;
>>   		}
>>   
>> -		if (task_on_rq_queued(p))
>> +		if (task_on_rq_queued(p)) {
>> +			update_rq_clock(rq);
>>   			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
>> -		else
>> +		} else {
>>   			p->wake_cpu = arg->dest_cpu;
>> +		}
>>   
>>   		/*
>>   		 * XXX __migrate_task() can fail, at which point we might end
> 
> So now you've got update_rq_clock() in both callers, why not remove it
> from __balance_push_cpu_stop() ?
> 
> Afaict nothing actually needs it before __migrate_task().
> 

Thanks for your review.
I'm afraid not, the rq clock also needs to be updated before
select_fallback_rq() is called.


> ---
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9435,8 +9435,6 @@ static int __balance_push_cpu_stop(void
>   	raw_spin_lock_irq(&p->pi_lock);
>   	rq_lock(rq, &rf);
>   
> -	update_rq_clock(rq);
> -
>   	if (task_rq(p) == rq && task_on_rq_queued(p)) {
>   		cpu = select_fallback_rq(rq->cpu, p);
>   		rq = __migrate_task(rq, &rf, p, cpu);

If we just remove update_rq_clock() from __balance_push_cpu_stop(), we 
will get this warning.


[ 1260.960166] rq->clock_update_flags < RQCF_ACT_SKIP
[ 1260.960170] WARNING: CPU: 25 PID: 196 at kernel/sched/sched.h:1496 
update_curr+0xf6/0x1f0

[ 1260.960318] Call Trace:
[ 1260.960320]  <TASK>
[ 1260.960323]  ? show_regs+0x5b/0x60
[ 1260.960327]  ? __warn+0x89/0x140
[ 1260.960331]  ? update_curr+0xf6/0x1f0
[ 1260.960334]  ? report_bug+0x1b7/0x1e0
[ 1260.960338]  ? __wake_up_klogd.part.25+0x5a/0x80
[ 1260.960342]  ? handle_bug+0x45/0x80
[ 1260.960346]  ? exc_invalid_op+0x18/0x70
[ 1260.960348]  ? asm_exc_invalid_op+0x1b/0x20
[ 1260.960354]  ? update_curr+0xf6/0x1f0
[ 1260.960356]  ? update_curr+0xf6/0x1f0
[ 1260.960359]  dequeue_entity+0x3b/0x410
[ 1260.960361]  dequeue_task_fair+0xc7/0x3c0
[ 1260.960363]  dequeue_task+0x30/0xf0
[ 1260.960365]  __do_set_cpus_allowed+0x94/0x130
[ 1260.960366]  do_set_cpus_allowed+0x38/0x60
[ 1260.960368]  cpuset_cpus_allowed_fallback+0x70/0x80
[ 1260.960372]  select_fallback_rq+0x20f/0x250            <----
[ 1260.960374]  __balance_push_cpu_stop+0x13f/0x1a0
[ 1260.960377]  ? migration_cpu_stop+0x2b0/0x2b0
[ 1260.960379]  cpu_stopper_thread+0xaf/0x140
[ 1260.960382]  smpboot_thread_fn+0x158/0x220
[ 1260.960387]  ? sort_range+0x30/0x30
[ 1260.960390]  kthread+0xfe/0x130
[ 1260.960392]  ? kthread_complete_and_exit+0x20/0x20
[ 1260.960394]  ret_from_fork+0x1f/0x30
[ 1260.960399]  </TASK>

Thanks,
Hao

Re: [External] Re: [PATCH v5 2/4] sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()

[Peter Zijlstra]

On Fri, Jun 16, 2023 at 03:56:25PM +0800, Hao Jia wrote:

> I'm afraid not, the rq clock also needs to be updated before
> select_fallback_rq() is called.

> If we just remove update_rq_clock() from __balance_push_cpu_stop(), we will
> get this warning.
> 
> 
> [ 1260.960166] rq->clock_update_flags < RQCF_ACT_SKIP
> [ 1260.960170] WARNING: CPU: 25 PID: 196 at kernel/sched/sched.h:1496
> update_curr+0xf6/0x1f0
> 
> [ 1260.960318] Call Trace:
> [ 1260.960320]  <TASK>
> [ 1260.960359]  dequeue_entity+0x3b/0x410
> [ 1260.960361]  dequeue_task_fair+0xc7/0x3c0
> [ 1260.960363]  dequeue_task+0x30/0xf0
> [ 1260.960365]  __do_set_cpus_allowed+0x94/0x130
> [ 1260.960366]  do_set_cpus_allowed+0x38/0x60
> [ 1260.960368]  cpuset_cpus_allowed_fallback+0x70/0x80
> [ 1260.960372]  select_fallback_rq+0x20f/0x250            <----

Urgh... :-(

[tip: sched/core] sched/core: Avoid multiple calling update_rq_clock() in __cfsb_csd_unthrottle()

[tip-bot2 for Hao Jia]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     ebb83d84e49b54369b0db67136a5fe1087124dcc
Gitweb:        https://git.kernel.org/tip/ebb83d84e49b54369b0db67136a5fe1087124dcc
Author:        Hao Jia <jiahao.os@bytedance.com>
AuthorDate:    Tue, 13 Jun 2023 16:20:11 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 16 Jun 2023 22:08:13 +02:00

sched/core: Avoid multiple calling update_rq_clock() in __cfsb_csd_unthrottle()

After commit 8ad075c2eb1f ("sched: Async unthrottling for cfs
bandwidth"), we may update the rq clock multiple times in the loop of
__cfsb_csd_unthrottle().

A prior (although less common) instance of this problem exists in
unthrottle_offline_cfs_rqs().

Cure both by ensuring update_rq_clock() is called before the loop and
setting RQCF_ACT_SKIP during the loop, to supress further updates.
The alternative would be pulling update_rq_clock() out of
unthrottle_cfs_rq(), but that gives an even bigger mess.

Fixes: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")
Reviewed-By: Ben Segall <bsegall@google.com>
Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20230613082012.49615-4-jiahao.os@bytedance.com
---
 kernel/sched/fair.c  | 18 ++++++++++++++++++
 kernel/sched/sched.h | 22 ++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7666dbc..a80a739 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5577,6 +5577,14 @@ static void __cfsb_csd_unthrottle(void *arg)
 	rq_lock(rq, &rf);
 
 	/*
+	 * Iterating over the list can trigger several call to
+	 * update_rq_clock() in unthrottle_cfs_rq().
+	 * Do it once and skip the potential next ones.
+	 */
+	update_rq_clock(rq);
+	rq_clock_start_loop_update(rq);
+
+	/*
 	 * Since we hold rq lock we're safe from concurrent manipulation of
 	 * the CSD list. However, this RCU critical section annotates the
 	 * fact that we pair with sched_free_group_rcu(), so that we cannot
@@ -5595,6 +5603,7 @@ static void __cfsb_csd_unthrottle(void *arg)
 
 	rcu_read_unlock();
 
+	rq_clock_stop_loop_update(rq);
 	rq_unlock(rq, &rf);
 }
 
@@ -6115,6 +6124,13 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
 
 	lockdep_assert_rq_held(rq);
 
+	/*
+	 * The rq clock has already been updated in the
+	 * set_rq_offline(), so we should skip updating
+	 * the rq clock again in unthrottle_cfs_rq().
+	 */
+	rq_clock_start_loop_update(rq);
+
 	rcu_read_lock();
 	list_for_each_entry_rcu(tg, &task_groups, list) {
 		struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
@@ -6137,6 +6153,8 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
 			unthrottle_cfs_rq(cfs_rq);
 	}
 	rcu_read_unlock();
+
+	rq_clock_stop_loop_update(rq);
 }
 
 #else /* CONFIG_CFS_BANDWIDTH */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 36e23e4..50d4b61 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1546,6 +1546,28 @@ static inline void rq_clock_cancel_skipupdate(struct rq *rq)
 	rq->clock_update_flags &= ~RQCF_REQ_SKIP;
 }
 
+/*
+ * During cpu offlining and rq wide unthrottling, we can trigger
+ * an update_rq_clock() for several cfs and rt runqueues (Typically
+ * when using list_for_each_entry_*)
+ * rq_clock_start_loop_update() can be called after updating the clock
+ * once and before iterating over the list to prevent multiple update.
+ * After the iterative traversal, we need to call rq_clock_stop_loop_update()
+ * to clear RQCF_ACT_SKIP of rq->clock_update_flags.
+ */
+static inline void rq_clock_start_loop_update(struct rq *rq)
+{
+	lockdep_assert_rq_held(rq);
+	SCHED_WARN_ON(rq->clock_update_flags & RQCF_ACT_SKIP);
+	rq->clock_update_flags |= RQCF_ACT_SKIP;
+}
+
+static inline void rq_clock_stop_loop_update(struct rq *rq)
+{
+	lockdep_assert_rq_held(rq);
+	rq->clock_update_flags &= ~RQCF_ACT_SKIP;
+}
+
 struct rq_flags {
 	unsigned long flags;
 	struct pin_cookie cookie;

[tip: sched/core] sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()

[tip-bot2 for Hao Jia]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     96500560f0c73c71bca1b27536c6254fa0e8ce37
Gitweb:        https://git.kernel.org/tip/96500560f0c73c71bca1b27536c6254fa0e8ce37
Author:        Hao Jia <jiahao.os@bytedance.com>
AuthorDate:    Tue, 13 Jun 2023 16:20:10 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 16 Jun 2023 22:08:12 +02:00

sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()

There is a double update_rq_clock() invocation:

  __balance_push_cpu_stop()
    update_rq_clock()
    __migrate_task()
      update_rq_clock()

Sadly select_fallback_rq() also needs update_rq_clock() for
__do_set_cpus_allowed(), it is not possible to remove the update from
__balance_push_cpu_stop(). So remove it from __migrate_task() and
ensure all callers of this function call update_rq_clock() prior to
calling it.

Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20230613082012.49615-3-jiahao.os@bytedance.com
---
 kernel/sched/core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 442efe5..c7db597 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2546,7 +2546,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
 	if (!is_cpu_allowed(p, dest_cpu))
 		return rq;
 
-	update_rq_clock(rq);
 	rq = move_queued_task(rq, rf, p, dest_cpu);
 
 	return rq;
@@ -2604,10 +2603,12 @@ static int migration_cpu_stop(void *data)
 				goto out;
 		}
 
-		if (task_on_rq_queued(p))
+		if (task_on_rq_queued(p)) {
+			update_rq_clock(rq);
 			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
-		else
+		} else {
 			p->wake_cpu = arg->dest_cpu;
+		}
 
 		/*
 		 * XXX __migrate_task() can fail, at which point we might end

[tip: sched/core] sched/core: Fixed missing rq clock update before calling set_rq_offline()

[tip-bot2 for Hao Jia]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     cab3ecaed5cdcc9c36a96874b4c45056a46ece45
Gitweb:        https://git.kernel.org/tip/cab3ecaed5cdcc9c36a96874b4c45056a46ece45
Author:        Hao Jia <jiahao.os@bytedance.com>
AuthorDate:    Tue, 13 Jun 2023 16:20:09 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 16 Jun 2023 22:08:12 +02:00

sched/core: Fixed missing rq clock update before calling set_rq_offline()

When using a cpufreq governor that uses
cpufreq_add_update_util_hook(), it is possible to trigger a missing
update_rq_clock() warning for the CPU hotplug path:

  rq_attach_root()
    set_rq_offline()
      rq_offline_rt()
	__disable_runtime()
	  sched_rt_rq_enqueue()
	    enqueue_top_rt_rq()
	      cpufreq_update_util()
		data->func(data, rq_clock(rq), flags)

Move update_rq_clock() from sched_cpu_deactivate() (one of it's
callers) into set_rq_offline() such that it covers all
set_rq_offline() usage.

Additionally change rq_attach_root() to use rq_lock_irqsave() so that
it will properly manage the runqueue clock flags.

Suggested-by: Ben Segall <bsegall@google.com>
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20230613082012.49615-2-jiahao.os@bytedance.com
---
 kernel/sched/core.c     | 2 +-
 kernel/sched/topology.c | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ac38225..442efe5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9585,6 +9585,7 @@ void set_rq_offline(struct rq *rq)
 	if (rq->online) {
 		const struct sched_class *class;
 
+		update_rq_clock(rq);
 		for_each_class(class) {
 			if (class->rq_offline)
 				class->rq_offline(rq);
@@ -9726,7 +9727,6 @@ int sched_cpu_deactivate(unsigned int cpu)
 
 	rq_lock_irqsave(rq, &rf);
 	if (rq->rd) {
-		update_rq_clock(rq);
 		BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
 		set_rq_offline(rq);
 	}
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index cb92dc5..d3a3b26 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -487,9 +487,9 @@ static void free_rootdomain(struct rcu_head *rcu)
 void rq_attach_root(struct rq *rq, struct root_domain *rd)
 {
 	struct root_domain *old_rd = NULL;
-	unsigned long flags;
+	struct rq_flags rf;
 
-	raw_spin_rq_lock_irqsave(rq, flags);
+	rq_lock_irqsave(rq, &rf);
 
 	if (rq->rd) {
 		old_rd = rq->rd;
@@ -515,7 +515,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
 	if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
 		set_rq_online(rq);
 
-	raw_spin_rq_unlock_irqrestore(rq, flags);
+	rq_unlock_irqrestore(rq, &rf);
 
 	if (old_rd)
 		call_rcu(&old_rd->rcu, free_rootdomain);

Re: [External] [tip: sched/core] sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()

[Hao Jia]

On 2023/6/19 tip-bot2 for Hao Jia wrote:
> The following commit has been merged into the sched/core branch of tip:
> 
> Commit-ID:     96500560f0c73c71bca1b27536c6254fa0e8ce37
> Gitweb:        https://git.kernel.org/tip/96500560f0c73c71bca1b27536c6254fa0e8ce37
> Author:        Hao Jia <jiahao.os@bytedance.com>
> AuthorDate:    Tue, 13 Jun 2023 16:20:10 +08:00
> Committer:     Peter Zijlstra <peterz@infradead.org>
> CommitterDate: Fri, 16 Jun 2023 22:08:12 +02:00
> 
> sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()
> 
> There is a double update_rq_clock() invocation:
> 
>    __balance_push_cpu_stop()
>      update_rq_clock()
>      __migrate_task()
>        update_rq_clock()
> 
> Sadly select_fallback_rq() also needs update_rq_clock() for
> __do_set_cpus_allowed(), it is not possible to remove the update from
> __balance_push_cpu_stop(). So remove it from __migrate_task() and
> ensure all callers of this function call update_rq_clock() prior to
> calling it.
> 
Hi Peter,

Thank you very much for refactoring these commit messages to make it 
clearer and more concise.

Thanks,
Hao

> Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> Link: https://lkml.kernel.org/r/20230613082012.49615-3-jiahao.os@bytedance.com
> ---
>   kernel/sched/core.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 442efe5..c7db597 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2546,7 +2546,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
>   	if (!is_cpu_allowed(p, dest_cpu))
>   		return rq;
>   
> -	update_rq_clock(rq);
>   	rq = move_queued_task(rq, rf, p, dest_cpu);
>   
>   	return rq;
> @@ -2604,10 +2603,12 @@ static int migration_cpu_stop(void *data)
>   				goto out;
>   		}
>   
> -		if (task_on_rq_queued(p))
> +		if (task_on_rq_queued(p)) {
> +			update_rq_clock(rq);
>   			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
> -		else
> +		} else {
>   			p->wake_cpu = arg->dest_cpu;
> +		}
>   
>   		/*
>   		 * XXX __migrate_task() can fail, at which point we might end