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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>

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

> ---
>  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
>