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Date:   Tue, 17 Jan 2023 13:16:21 +0000
From:   Mark Rutland <mark.rutland@arm.com>
To:     Peter Zijlstra <peterz@infradead.org>
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Subject: Re: [PATCH v3 00/51] cpuidle,rcu: Clean up the mess
Message-ID: <Y8afpbHtDOqAHq9M@FVFF77S0Q05N.cambridge.arm.com>
References: <20230112194314.845371875@infradead.org>
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On Tue, Jan 17, 2023 at 11:26:29AM +0100, Peter Zijlstra wrote:
> On Mon, Jan 16, 2023 at 04:59:04PM +0000, Mark Rutland wrote:
> 
> > I'm sorry to have to bear some bad news on that front. :(
> 
> Moo, something had to give..
> 
> 
> > IIUC what's happenign here is the PSCI cpuidle driver has entered idle and RCU
> > is no longer watching when arm64's cpu_suspend() manipulates DAIF. Our
> > local_daif_*() helpers poke lockdep and tracing, hence the call to
> > trace_hardirqs_off() and the RCU usage.
> 
> Right, strictly speaking not needed at this point, IRQs should have been
> traced off a long time ago.

True, but there are some other calls around here that *might* end up invoking
RCU stuff (e.g. the MTE code).

That all needs a noinstr cleanup too, which I'll sort out as a follow-up.

> > I think we need RCU to be watching all the way down to cpu_suspend(), and it's
> > cpu_suspend() that should actually enter/exit idle context. That and we need to
> > make cpu_suspend() and the low-level PSCI invocation noinstr.
> > 
> > I'm not sure whether 32-bit will have a similar issue or not.
> 
> I'm not seeing 32bit or Risc-V have similar issues here, but who knows,
> maybe I missed somsething.

I reckon if they do, the core changes here give us the infrastructure to fix
them if/when we get reports.

> In any case, the below ought to cure the ARM64 case and remove that last
> known RCU_NONIDLE() user as a bonus.

The below works for me testing on a Juno R1 board with PSCI, using defconfig +
CONFIG_PROVE_LOCKING=y + CONFIG_DEBUG_LOCKDEP=y + CONFIG_DEBUG_ATOMIC_SLEEP=y.
I'm not sure how to test the LPI / FFH part, but it looks good to me.

FWIW:

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>

Sudeep, would you be able to give the LPI/FFH side a spin with the kconfig
options above?

Thanks,
Mark.

> 
> ---
> diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
> index 41974a1a229a..42e19fff40ee 100644
> --- a/arch/arm64/kernel/cpuidle.c
> +++ b/arch/arm64/kernel/cpuidle.c
> @@ -67,10 +67,10 @@ __cpuidle int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
>  	u32 state = lpi->address;
>  
>  	if (ARM64_LPI_IS_RETENTION_STATE(lpi->arch_flags))
> -		return CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM(psci_cpu_suspend_enter,
> +		return CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM_RCU(psci_cpu_suspend_enter,
>  						lpi->index, state);
>  	else
> -		return CPU_PM_CPU_IDLE_ENTER_PARAM(psci_cpu_suspend_enter,
> +		return CPU_PM_CPU_IDLE_ENTER_PARAM_RCU(psci_cpu_suspend_enter,
>  					     lpi->index, state);
>  }
>  #endif
> diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
> index e7163f31f716..0fbdf5fe64d8 100644
> --- a/arch/arm64/kernel/suspend.c
> +++ b/arch/arm64/kernel/suspend.c
> @@ -4,6 +4,7 @@
>  #include <linux/slab.h>
>  #include <linux/uaccess.h>
>  #include <linux/pgtable.h>
> +#include <linux/cpuidle.h>
>  #include <asm/alternative.h>
>  #include <asm/cacheflush.h>
>  #include <asm/cpufeature.h>
> @@ -104,6 +105,10 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
>  	 * From this point debug exceptions are disabled to prevent
>  	 * updates to mdscr register (saved and restored along with
>  	 * general purpose registers) from kernel debuggers.
> +	 *
> +	 * Strictly speaking the trace_hardirqs_off() here is superfluous,
> +	 * hardirqs should be firmly off by now. This really ought to use
> +	 * something like raw_local_daif_save().
>  	 */
>  	flags = local_daif_save();
>  
> @@ -120,6 +125,8 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
>  	 */
>  	arm_cpuidle_save_irq_context(&context);
>  
> +	ct_cpuidle_enter();
> +
>  	if (__cpu_suspend_enter(&state)) {
>  		/* Call the suspend finisher */
>  		ret = fn(arg);
> @@ -133,8 +140,11 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
>  		 */
>  		if (!ret)
>  			ret = -EOPNOTSUPP;
> +
> +		ct_cpuidle_exit();
>  	} else {
> -		RCU_NONIDLE(__cpu_suspend_exit());
> +		ct_cpuidle_exit();
> +		__cpu_suspend_exit();
>  	}
>  
>  	arm_cpuidle_restore_irq_context(&context);
> diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
> index 4fc4e0381944..312a34ef28dc 100644
> --- a/drivers/cpuidle/cpuidle-psci.c
> +++ b/drivers/cpuidle/cpuidle-psci.c
> @@ -69,16 +69,12 @@ static __cpuidle int __psci_enter_domain_idle_state(struct cpuidle_device *dev,
>  	else
>  		pm_runtime_put_sync_suspend(pd_dev);
>  
> -	ct_cpuidle_enter();
> -
>  	state = psci_get_domain_state();
>  	if (!state)
>  		state = states[idx];
>  
>  	ret = psci_cpu_suspend_enter(state) ? -1 : idx;
>  
> -	ct_cpuidle_exit();
> -
>  	if (s2idle)
>  		dev_pm_genpd_resume(pd_dev);
>  	else
> @@ -192,7 +188,7 @@ static __cpuidle int psci_enter_idle_state(struct cpuidle_device *dev,
>  {
>  	u32 *state = __this_cpu_read(psci_cpuidle_data.psci_states);
>  
> -	return CPU_PM_CPU_IDLE_ENTER_PARAM(psci_cpu_suspend_enter, idx, state[idx]);
> +	return CPU_PM_CPU_IDLE_ENTER_PARAM_RCU(psci_cpu_suspend_enter, idx, state[idx]);
>  }
>  
>  static const struct of_device_id psci_idle_state_match[] = {
> diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> index e7bcfca4159f..f3a044fa4652 100644
> --- a/drivers/firmware/psci/psci.c
> +++ b/drivers/firmware/psci/psci.c
> @@ -462,11 +462,22 @@ int psci_cpu_suspend_enter(u32 state)
>  	if (!psci_power_state_loses_context(state)) {
>  		struct arm_cpuidle_irq_context context;
>  
> +		ct_cpuidle_enter();
>  		arm_cpuidle_save_irq_context(&context);
>  		ret = psci_ops.cpu_suspend(state, 0);
>  		arm_cpuidle_restore_irq_context(&context);
> +		ct_cpuidle_exit();
>  	} else {
> +		/*
> +		 * ARM64 cpu_suspend() wants to do ct_cpuidle_*() itself.
> +		 */
> +		if (!IS_ENABLED(CONFIG_ARM64))
> +			ct_cpuidle_enter();
> +
>  		ret = cpu_suspend(state, psci_suspend_finisher);
> +
> +		if (!IS_ENABLED(CONFIG_ARM64))
> +			ct_cpuidle_exit();
>  	}
>  
>  	return ret;
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index 630c879143c7..3183aeb7f5b4 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -307,7 +307,7 @@ extern s64 cpuidle_governor_latency_req(unsigned int cpu);
>  #define __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter,			\
>  				idx,					\
>  				state,					\
> -				is_retention)				\
> +				is_retention, is_rcu)			\
>  ({									\
>  	int __ret = 0;							\
>  									\
> @@ -319,9 +319,11 @@ extern s64 cpuidle_governor_latency_req(unsigned int cpu);
>  	if (!is_retention)						\
>  		__ret =  cpu_pm_enter();				\
>  	if (!__ret) {							\
> -		ct_cpuidle_enter();					\
> +		if (!is_rcu)						\
> +			ct_cpuidle_enter();				\
>  		__ret = low_level_idle_enter(state);			\
> -		ct_cpuidle_exit();					\
> +		if (!is_rcu)						\
> +			ct_cpuidle_exit();				\
>  		if (!is_retention)					\
>  			cpu_pm_exit();					\
>  	}								\
> @@ -330,15 +332,21 @@ extern s64 cpuidle_governor_latency_req(unsigned int cpu);
>  })
>  
>  #define CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx)	\
> -	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 0)
> +	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 0, 0)
>  
>  #define CPU_PM_CPU_IDLE_ENTER_RETENTION(low_level_idle_enter, idx)	\
> -	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 1)
> +	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 1, 0)
>  
>  #define CPU_PM_CPU_IDLE_ENTER_PARAM(low_level_idle_enter, idx, state)	\
> -	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 0)
> +	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 0, 0)
> +
> +#define CPU_PM_CPU_IDLE_ENTER_PARAM_RCU(low_level_idle_enter, idx, state)	\
> +	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 0, 1)
>  
>  #define CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM(low_level_idle_enter, idx, state)	\
> -	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 1)
> +	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 1, 0)
> +
> +#define CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM_RCU(low_level_idle_enter, idx, state)	\
> +	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 1, 1)
>  
>  #endif /* _LINUX_CPUIDLE_H */