Re: [PATCHv2 4/5] irqchip/GICv3: let gic_handle_irq() utilize irqentry on arm64

From: Mark Rutland <mark.rutland@arm.com>
To: Pingfan Liu <kernelfans@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Joey Gouly <joey.gouly@arm.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Julien Thierry <julien.thierry@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Yuichi Ito <ito-yuichi@fujitsu.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCHv2 4/5] irqchip/GICv3: let gic_handle_irq() utilize irqentry on arm64
Date: Tue, 28 Sep 2021 10:10:53 +0100	[thread overview]
Message-ID: <20210928091053.GD1924@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20210924132837.45994-5-kernelfans@gmail.com>

On Fri, Sep 24, 2021 at 09:28:36PM +0800, Pingfan Liu wrote:
> The call to rcu_irq_enter() originated from gic_handle_irq() is
> redundant now, since arm64 has enter_from_kernel_mode() akin to
> irqenter_entry(), which has already called rcu_irq_enter().

Here I think you're referring to the call in handle_domain_irq(), but
that isn't clear from the commit message.

> Based on code analysis, the redundant can raise some mistake, e.g.
> rcu_data->dynticks_nmi_nesting inc 2, which causes
> rcu_is_cpu_rrupt_from_idle() unexpected.
> 
> So eliminate the call to irq_enter() in handle_domain_irq(). And
> accordingly supplementing irq_enter_rcu().

We support many more irqchips on arm64, and GICv3 can be used on regular
32-bit arm, so this isn't right. Moving the irq_enter_rcu() call
into the GICv3 driver specifically breaks other drivers on arm64 by
removing the call, and breaks the GICv3 driver on arm by adding a
duplicate call.

It looks like this should live in do_interrupt_handler() in
arch/arm64/kernel/entry-common.c, e.g.

| static void do_interrupt_handler(struct pt_regs *regs,
| 				 void (*handler)(struct pt_regs *)) 
| {
| 	irq_enter_rcu();
| 	if (on_thread_stack())
| 		call_on_irq_stack(regs, handler);
| 	else
| 		handler(regs);
| 	irq_exit_rcu();
| }

... unless there's some problem with that?

Thanks,
Mark.

> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Joey Gouly <joey.gouly@arm.com>
> Cc: Sami Tolvanen <samitolvanen@google.com>
> Cc: Julien Thierry <julien.thierry@arm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Yuichi Ito <ito-yuichi@fujitsu.com>
> Cc: linux-kernel@vger.kernel.org
> To: linux-arm-kernel@lists.infradead.org
> ---
>  arch/arm64/Kconfig           | 1 +
>  drivers/irqchip/irq-gic-v3.c | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 5c7ae4c3954b..d29bae38a951 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -98,6 +98,7 @@ config ARM64
>  	select ARCH_HAS_UBSAN_SANITIZE_ALL
>  	select ARM_AMBA
>  	select ARM_ARCH_TIMER
> +	select HAVE_ARCH_IRQENTRY
>  	select ARM_GIC
>  	select AUDIT_ARCH_COMPAT_GENERIC
>  	select ARM_GIC_V2M if PCI
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 89dcec902a82..906538fa8771 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -729,10 +729,12 @@ static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs
>  	else
>  		isb();
>  
> +	irq_enter_rcu();
>  	if (handle_domain_irq(gic_data.domain, irqnr, regs)) {
>  		WARN_ONCE(true, "Unexpected interrupt received!\n");
>  		gic_deactivate_unhandled(irqnr);
>  	}
> +	irq_exit_rcu();
>  }
>  
>  static u32 gic_get_pribits(void)
> -- 
> 2.31.1
> 