Re: [PATCH 01/15] irq: mips: avoid nested irq_enter()

From: Marc Zyngier <maz@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-kernel@vger.kernel.org, aou@eecs.berkeley.edu,
	catalin.marinas@arm.com, deanbo422@gmail.com, green.hu@gmail.com,
	guoren@kernel.org, jonas@southpole.se, kernelfans@gmail.com,
	linux-arm-kernel@lists.infradead.org, linux@armlinux.org.uk,
	nickhu@andestech.com, palmer@dabbelt.com, paulmck@kernel.org,
	paul.walmsley@sifive.com, peterz@infradead.org, shorne@gmail.com,
	stefan.kristiansson@saunalahti.fi, tglx@linutronix.de,
	torvalds@linux-foundation.org, tsbogend@alpha.franken.de,
	vgupta@kernel.org, will@kernel.org
Subject: Re: [PATCH 01/15] irq: mips: avoid nested irq_enter()
Date: Fri, 22 Oct 2021 11:38:23 +0100	[thread overview]
Message-ID: <87mtn1bazk.wl-maz@kernel.org> (raw)
In-Reply-To: <20211021180236.37428-2-mark.rutland@arm.com>

On Thu, 21 Oct 2021 19:02:22 +0100,
Mark Rutland <mark.rutland@arm.com> wrote:
> 
> As bcm6345_l1_irq_handle() is a chained irqchip handler, it will be
> invoked within the context of the root irqchip handler, which must have
> entered IRQ context already.
> 
> When bcm6345_l1_irq_handle() calls arch/mips's do_IRQ() , this will nest
> another call to irq_enter(), and the resulting nested increment to
> `rcu_data.dynticks_nmi_nesting` will cause rcu_is_cpu_rrupt_from_idle()
> to fail to identify wakeups from idle, resulting in failure to preempt,
> and RCU stalls.
> 
> Chained irqchip handlers must invoke IRQ handlers by way of thee core
> irqchip code, i.e. generic_handle_irq() or generic_handle_domain_irq()
> and should not call do_IRQ(), which is intended only for root irqchip
> handlers.
> 
> Fix bcm6345_l1_irq_handle() by calling generic_handle_irq() directly.
> 
> Fixes: c7c42ec2baa1de7a ("irqchips/bmips: Add bcm6345-l1 interrupt controller")
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> ---
>  drivers/irqchip/irq-bcm6345-l1.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-bcm6345-l1.c b/drivers/irqchip/irq-bcm6345-l1.c
> index e3483789f4df..1bd0621c4ce2 100644
> --- a/drivers/irqchip/irq-bcm6345-l1.c
> +++ b/drivers/irqchip/irq-bcm6345-l1.c
> @@ -140,7 +140,7 @@ static void bcm6345_l1_irq_handle(struct irq_desc *desc)
>  		for_each_set_bit(hwirq, &pending, IRQS_PER_WORD) {
>  			irq = irq_linear_revmap(intc->domain, base + hwirq);
>  			if (irq)
> -				do_IRQ(irq);
> +				generic_handle_irq(irq);
>  			else
>  				spurious_interrupt();
>  		}

A marginally better fix would be to have:

diff --git a/drivers/irqchip/irq-bcm6345-l1.c b/drivers/irqchip/irq-bcm6345-l1.c
index 1bd0621c4ce2..fd079215c17f 100644
--- a/drivers/irqchip/irq-bcm6345-l1.c
+++ b/drivers/irqchip/irq-bcm6345-l1.c
@@ -132,16 +132,12 @@ static void bcm6345_l1_irq_handle(struct irq_desc *desc)
 		int base = idx * IRQS_PER_WORD;
 		unsigned long pending;
 		irq_hw_number_t hwirq;
-		unsigned int irq;
 
 		pending = __raw_readl(cpu->map_base + reg_status(intc, idx));
 		pending &= __raw_readl(cpu->map_base + reg_enable(intc, idx));
 
 		for_each_set_bit(hwirq, &pending, IRQS_PER_WORD) {
-			irq = irq_linear_revmap(intc->domain, base + hwirq);
-			if (irq)
-				generic_handle_irq(irq);
-			else
+			if (generic_handle_domain_irq(intc->domain, base + hwirq))
 				spurious_interrupt();
 		}
 	}

but we can also tackle that separately if you'd rather keep the change
minimal.

	M.

-- 
Without deviation from the norm, progress is not possible.

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