Re: [PATCH] ARM: OMAP2+: Fix suspcious RCU usage splats for omap_enter_idle_coupled

["Paul E. McKenney" <paulmck@kernel.org>]

On Fri, Jan 08, 2021 at 03:41:05PM +0200, Tony Lindgren wrote:
> We get suspcious RCU usage splats with cpuidle in several places in
> omap_enter_idle_coupled() with the kernel debug options enabled:
> 
> RCU used illegally from extended quiescent state!
> ...
> (_raw_spin_lock_irqsave)
> (omap_enter_idle_coupled+0x17c/0x2d8)
> (omap_enter_idle_coupled)
> (cpuidle_enter_state)
> (cpuidle_enter_state_coupled)
> (cpuidle_enter)
> 
> Let's use RCU_NONIDLE to suppress these splats. Things got changed around
> with commit 1098582a0f6c ("sched,idle,rcu: Push rcu_idle deeper into the
> idle path") that started triggering these warnings.
> 
> For the tick_broadcast related calls, ideally we'd just switch over to
> using CPUIDLE_FLAG_TIMER_STOP for omap_enter_idle_coupled() to have the
> generic cpuidle code handle the tick_broadcast related calls for us and
> then just drop the tick_broadcast calls here.
> 
> But we're currently missing the call in the common cpuidle code for
> tick_broadcast_enable() that CPU1 hotplug needs as described in earlier
> commit 50d6b3cf9403 ("ARM: OMAP2+: fix lack of timer interrupts on CPU1
> after hotplug").
> 
> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Russell King <rmk+kernel@armlinux.org.uk>
> Signed-off-by: Tony Lindgren <tony@atomide.com>

From an RCU viewpoint:

Acked-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  arch/arm/mach-omap2/cpuidle44xx.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/mach-omap2/cpuidle44xx.c b/arch/arm/mach-omap2/cpuidle44xx.c
> --- a/arch/arm/mach-omap2/cpuidle44xx.c
> +++ b/arch/arm/mach-omap2/cpuidle44xx.c
> @@ -151,10 +151,10 @@ static int omap_enter_idle_coupled(struct cpuidle_device *dev,
>  				 (cx->mpu_logic_state == PWRDM_POWER_OFF);
>  
>  	/* Enter broadcast mode for periodic timers */
> -	tick_broadcast_enable();
> +	RCU_NONIDLE(tick_broadcast_enable());
>  
>  	/* Enter broadcast mode for one-shot timers */
> -	tick_broadcast_enter();
> +	RCU_NONIDLE(tick_broadcast_enter());
>  
>  	/*
>  	 * Call idle CPU PM enter notifier chain so that
> @@ -166,7 +166,7 @@ static int omap_enter_idle_coupled(struct cpuidle_device *dev,
>  
>  	if (dev->cpu == 0) {
>  		pwrdm_set_logic_retst(mpu_pd, cx->mpu_logic_state);
> -		omap_set_pwrdm_state(mpu_pd, cx->mpu_state);
> +		RCU_NONIDLE(omap_set_pwrdm_state(mpu_pd, cx->mpu_state));
>  
>  		/*
>  		 * Call idle CPU cluster PM enter notifier chain
> @@ -179,7 +179,7 @@ static int omap_enter_idle_coupled(struct cpuidle_device *dev,
>  				index = 1;
>  				cx = state_ptr + index;
>  				pwrdm_set_logic_retst(mpu_pd, cx->mpu_logic_state);
> -				omap_set_pwrdm_state(mpu_pd, cx->mpu_state);
> +				RCU_NONIDLE(omap_set_pwrdm_state(mpu_pd, cx->mpu_state));
>  				mpuss_can_lose_context = 0;
>  			}
>  		}
> @@ -195,9 +195,9 @@ static int omap_enter_idle_coupled(struct cpuidle_device *dev,
>  		    mpuss_can_lose_context)
>  			gic_dist_disable();
>  
> -		clkdm_deny_idle(cpu_clkdm[1]);
> -		omap_set_pwrdm_state(cpu_pd[1], PWRDM_POWER_ON);
> -		clkdm_allow_idle(cpu_clkdm[1]);
> +		RCU_NONIDLE(clkdm_deny_idle(cpu_clkdm[1]));
> +		RCU_NONIDLE(omap_set_pwrdm_state(cpu_pd[1], PWRDM_POWER_ON));
> +		RCU_NONIDLE(clkdm_allow_idle(cpu_clkdm[1]));
>  
>  		if (IS_PM44XX_ERRATUM(PM_OMAP4_ROM_SMP_BOOT_ERRATUM_GICD) &&
>  		    mpuss_can_lose_context) {
> @@ -225,7 +225,7 @@ static int omap_enter_idle_coupled(struct cpuidle_device *dev,
>  	cpu_pm_exit();
>  
>  cpu_pm_out:
> -	tick_broadcast_exit();
> +	RCU_NONIDLE(tick_broadcast_exit());
>  
>  fail:
>  	cpuidle_coupled_parallel_barrier(dev, &abort_barrier);
> -- 
> 2.30.0

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