[PATCH v3 0/4] Fix some warnings about rq clock

[PATCH v3 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.

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.

[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     |  7 ++++---
 kernel/sched/fair.c     | 18 ++++++++++++++++++
 kernel/sched/sched.h    | 21 +++++++++++++++++++++
 kernel/sched/topology.c | 10 ++++++----
 4 files changed, 49 insertions(+), 7 deletions(-)

-- 
2.37.0

[PATCH v3 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 set_rq_offline() we need to update the rq clock to avoid
using the old rq clock, and use rq_lock_irqsave()/rq_unlock_irqrestore()
to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore() 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

Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
---
 kernel/sched/topology.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 6682535e37c8..b89497696880 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -487,15 +487,17 @@ 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;
 
-		if (cpumask_test_cpu(rq->cpu, old_rd->online))
+		if (cpumask_test_cpu(rq->cpu, old_rd->online)) {
+			update_rq_clock(rq);
 			set_rq_offline(rq);
+		}
 
 		cpumask_clear_cpu(rq->cpu, old_rd->span);
 
@@ -515,7 +517,7 @@ 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);
-- 
2.37.0

[PATCH v3 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>
---
 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 944c3ae39861..2bcf6a8e71fc 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
-- 
2.37.0

[PATCH v3 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>
---
 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;
-- 
2.37.0

[PATCH v3 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 before the set_rq_offline()
function runs, 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>
---
 kernel/sched/fair.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index af9604f4b135..9e961e0ec971 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 before the
+	 * set_rq_offline() runs, 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 */
-- 
2.37.0

Re: [PATCH v3 1/4] sched/core: Fixed missing rq clock update before calling set_rq_offline()

[Vincent Guittot]

On Mon, 15 May 2023 at 08:39, Hao Jia <jiahao.os@bytedance.com> 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 set_rq_offline() we need to update the rq clock to avoid
> using the old rq clock, and use rq_lock_irqsave()/rq_unlock_irqrestore()
> to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore() 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
>
> Signed-off-by: Hao Jia <jiahao.os@bytedance.com>

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

> ---
>  kernel/sched/topology.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 6682535e37c8..b89497696880 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -487,15 +487,17 @@ 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;
>
> -               if (cpumask_test_cpu(rq->cpu, old_rd->online))
> +               if (cpumask_test_cpu(rq->cpu, old_rd->online)) {
> +                       update_rq_clock(rq);
>                         set_rq_offline(rq);
> +               }
>
>                 cpumask_clear_cpu(rq->cpu, old_rd->span);
>
> @@ -515,7 +517,7 @@ 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);
> --
> 2.37.0
>

Re: [PATCH v3 2/4] sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()

[Vincent Guittot]

On Mon, 15 May 2023 at 08:39, Hao Jia <jiahao.os@bytedance.com> wrote:
>
> 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 944c3ae39861..2bcf6a8e71fc 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
> --
> 2.37.0
>

Re: [PATCH v3 3/4] sched/core: Avoid multiple calling update_rq_clock() in __cfsb_csd_unthrottle()

[Vincent Guittot]

On Mon, 15 May 2023 at 08:39, Hao Jia <jiahao.os@bytedance.com> wrote:
>
> 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;
> --
> 2.37.0
>

Re: [PATCH v3 4/4] sched/core: Avoid multiple calling update_rq_clock() in unthrottle_offline_cfs_rqs()

[Vincent Guittot]

On Mon, 15 May 2023 at 08:39, Hao Jia <jiahao.os@bytedance.com> wrote:
>
> 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 before the set_rq_offline()
> function runs, 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..9e961e0ec971 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 before the
> +        * set_rq_offline() runs, 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 */
> --
> 2.37.0
>

Re: [PATCH v3 0/4] Fix some warnings about rq clock

[Hao Jia]

kindly ping...


On 2023/5/15 Hao Jia wrote:
> 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.
> 
> 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.
> 
> [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     |  7 ++++---
>   kernel/sched/fair.c     | 18 ++++++++++++++++++
>   kernel/sched/sched.h    | 21 +++++++++++++++++++++
>   kernel/sched/topology.c | 10 ++++++----
>   4 files changed, 49 insertions(+), 7 deletions(-)
> 

Re: [PATCH v3 0/4] Fix some warnings about rq clock

[Hao Jia]

Kindly ping, any comment?

Thanks,
Hao

On 2023/5/15 Hao Jia wrote:
> 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.
> 
> 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.
> 
> [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     |  7 ++++---
>   kernel/sched/fair.c     | 18 ++++++++++++++++++
>   kernel/sched/sched.h    | 21 +++++++++++++++++++++
>   kernel/sched/topology.c | 10 ++++++----
>   4 files changed, 49 insertions(+), 7 deletions(-)
>