Re: [PATCH 4.19 00/29] 4.19.282-rc1 review

[Naresh Kamboju]

Hi Steven,

On Wed, 26 Apr 2023 at 23:14, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Wed, 26 Apr 2023 17:09:45 -0400
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> > Now the question is, why is this triggering on 4.19 but not in latest
> > mainline?
>
> I found it, I backported this patch and the warning goes away (at least for
> me). Can you add this and see if it makes the warning go away for you too?

I have applied this patch on stable-rc 4.19 branch and tested on
- arm64: Juno-r2
 - x86_64 device

and the reported problem has been resolved.

Thanks for finding a quick fix patch.

>
> -- Steve
>
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Date: Fri, 7 Aug 2020 20:50:19 +0200
> Subject: [PATCH] sched,idle,rcu: Push rcu_idle deeper into the idle path
>
> commit 1098582a0f6c4e8fd28da0a6305f9233d02c9c1d upstream.
>
> Lots of things take locks, due to a wee bug, rcu_lockdep didn't notice
> that the locking tracepoints were using RCU.
>
> Push rcu_idle_{enter,exit}() as deep as possible into the idle paths,
> this also resolves a lot of _rcuidle()/RCU_NONIDLE() usage.
>
> Specifically, sched_clock_idle_wakeup_event() will use ktime which
> will use seqlocks which will tickle lockdep, and
> stop_critical_timings() uses lock.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> Tested-by: Marco Elver <elver@xxxxxxxxxx>
> Link: https://lkml.kernel.org/r/20200821085348.310943801@xxxxxxxxxxxxx


Tested-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
Tested-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>

test log:
  - https://lkft.validation.linaro.org/scheduler/job/6380295#L1418
  - https://lkft.validation.linaro.org/scheduler/job/6380303#L1443

> ---
>  drivers/cpuidle/cpuidle.c | 12 ++++++++----
>  kernel/sched/idle.c       | 22 ++++++++--------------
>  2 files changed, 16 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 2d182dc1b49e..01bde6dec13a 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -140,13 +140,14 @@ static void enter_s2idle_proper(struct cpuidle_driver *drv,
>          * executing it contains RCU usage regarded as invalid in the idle
>          * context, so tell RCU about that.
>          */
> -       RCU_NONIDLE(tick_freeze());
> +       tick_freeze();
>         /*
>          * The state used here cannot be a "coupled" one, because the "coupled"
>          * cpuidle mechanism enables interrupts and doing that with timekeeping
>          * suspended is generally unsafe.
>          */
>         stop_critical_timings();
> +       rcu_idle_enter();
>         drv->states[index].enter_s2idle(dev, drv, index);
>         if (WARN_ON_ONCE(!irqs_disabled()))
>                 local_irq_disable();
> @@ -155,7 +156,8 @@ static void enter_s2idle_proper(struct cpuidle_driver *drv,
>          * first CPU executing it calls functions containing RCU read-side
>          * critical sections, so tell RCU about that.
>          */
> -       RCU_NONIDLE(tick_unfreeze());
> +       rcu_idle_exit();
> +       tick_unfreeze();
>         start_critical_timings();
>
>         time_end = ns_to_ktime(local_clock());
> @@ -224,16 +226,18 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
>         /* Take note of the planned idle state. */
>         sched_idle_set_state(target_state);
>
> -       trace_cpu_idle_rcuidle(index, dev->cpu);
> +       trace_cpu_idle(index, dev->cpu);
>         time_start = ns_to_ktime(local_clock());
>
>         stop_critical_timings();
> +       rcu_idle_enter();
>         entered_state = target_state->enter(dev, drv, index);
> +       rcu_idle_exit();
>         start_critical_timings();
>
>         sched_clock_idle_wakeup_event();
>         time_end = ns_to_ktime(local_clock());
> -       trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
> +       trace_cpu_idle(PWR_EVENT_EXIT, dev->cpu);
>
>         /* The cpu is no longer idle or about to enter idle. */
>         sched_idle_set_state(NULL);
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 44a17366c8ec..4e3d149d64ad 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -53,17 +53,18 @@ __setup("hlt", cpu_idle_nopoll_setup);
>
>  static noinline int __cpuidle cpu_idle_poll(void)
>  {
> +       trace_cpu_idle(0, smp_processor_id());
> +       stop_critical_timings();
>         rcu_idle_enter();
> -       trace_cpu_idle_rcuidle(0, smp_processor_id());
>         local_irq_enable();
> -       stop_critical_timings();
>
>         while (!tif_need_resched() &&
> -               (cpu_idle_force_poll || tick_check_broadcast_expired()))
> +              (cpu_idle_force_poll || tick_check_broadcast_expired()))
>                 cpu_relax();
> -       start_critical_timings();
> -       trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
> +
>         rcu_idle_exit();
> +       start_critical_timings();
> +       trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
>
>         return 1;
>  }
> @@ -90,7 +91,9 @@ void __cpuidle default_idle_call(void)
>                 local_irq_enable();
>         } else {
>                 stop_critical_timings();
> +               rcu_idle_enter();
>                 arch_cpu_idle();
> +               rcu_idle_exit();
>                 start_critical_timings();
>         }
>  }
> @@ -148,7 +151,6 @@ static void cpuidle_idle_call(void)
>
>         if (cpuidle_not_available(drv, dev)) {
>                 tick_nohz_idle_stop_tick();
> -               rcu_idle_enter();
>
>                 default_idle_call();
>                 goto exit_idle;
> @@ -166,19 +168,15 @@ static void cpuidle_idle_call(void)
>
>         if (idle_should_enter_s2idle() || dev->use_deepest_state) {
>                 if (idle_should_enter_s2idle()) {
> -                       rcu_idle_enter();
>
>                         entered_state = cpuidle_enter_s2idle(drv, dev);
>                         if (entered_state > 0) {
>                                 local_irq_enable();
>                                 goto exit_idle;
>                         }
> -
> -                       rcu_idle_exit();
>                 }
>
>                 tick_nohz_idle_stop_tick();
> -               rcu_idle_enter();
>
>                 next_state = cpuidle_find_deepest_state(drv, dev);
>                 call_cpuidle(drv, dev, next_state);
> @@ -195,8 +193,6 @@ static void cpuidle_idle_call(void)
>                 else
>                         tick_nohz_idle_retain_tick();
>
> -               rcu_idle_enter();
> -
>                 entered_state = call_cpuidle(drv, dev, next_state);
>                 /*
>                  * Give the governor an opportunity to reflect on the outcome
> @@ -212,8 +208,6 @@ static void cpuidle_idle_call(void)
>          */
>         if (WARN_ON_ONCE(irqs_disabled()))
>                 local_irq_enable();
> -
> -       rcu_idle_exit();
>  }
>
>  /*
> --
> 2.39.2

- Naresh


--
Linaro LKFT
https://lkft.linaro.org