linux-kernel - Re: [PATCHv3 1/3] kernel/irq: make irq_{enter,exit}() in handle_domain

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Message-ID: <87sfxlrtqz.wl-maz@kernel.org>
Date:   Fri, 01 Oct 2021 10:15:16 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Joey Gouly <joey.gouly@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Julien Thierry <julien.thierry@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yuichi Ito <ito-yuichi@...itsu.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 1/3] kernel/irq: make irq_{enter,exit}() in handle_domain_irq() arch optional

On Thu, 30 Sep 2021 14:17:06 +0100,
Pingfan Liu <kernelfans@...il.com> wrote:
> 
> When an IRQ is taken, some accounting needs to be performed to enter and
> exit IRQ context around the IRQ handler. Historically arch code would
> leave this to the irqchip or core IRQ code, but these days we want this
> to happen in exception entry code, and architectures such as arm64 do
> this.
> 
> Currently handle_domain_irq() performs this entry/exit accounting, and
> if used on an architecture where the entry code also does this, the
> entry/exit accounting will be performed twice per IRQ. This is
> problematic as core RCU code such as rcu_is_cpu_rrupt_from_idle()
> depends on this happening once per IRQ, and will not detect quescent
> periods correctly, leading to stall warnings.
> 
> As irqchip drivers which use handle_domain_irq() need to work on
> architectures with or without their own entry/exit accounting, this
> patch makes handle_domain_irq() conditionally perform the entry
> accounting depending on a new HAVE_ARCH_IRQENTRY Kconfig symbol that
> architectures can select if they perform this entry accounting
> themselves.
> 
> For architectures which do not select the symbol. there should be no
> functional change as a result of this patch.
> 
> Signed-off-by: Pingfan Liu <kernelfans@...il.com>
> Reviewed-by: Mark Rutland <mark.rutland@....com>
> Cc: "Paul E. McKenney" <paulmck@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Joey Gouly <joey.gouly@....com>
> Cc: Sami Tolvanen <samitolvanen@...gle.com>
> Cc: Julien Thierry <julien.thierry@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Yuichi Ito <ito-yuichi@...itsu.com>
> Cc: linux-kernel@...r.kernel.org
> To: linux-arm-kernel@...ts.infradead.org
> ---
>  kernel/irq/Kconfig   | 3 +++
>  kernel/irq/irqdesc.c | 4 ++++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
> index fbc54c2a7f23..defa1db2d664 100644
> --- a/kernel/irq/Kconfig
> +++ b/kernel/irq/Kconfig
> @@ -100,6 +100,9 @@ config IRQ_MSI_IOMMU
>  config HANDLE_DOMAIN_IRQ
>  	bool
>  
> +config HAVE_ARCH_IRQENTRY
> +	bool
> +
>  config IRQ_TIMINGS
>  	bool
>  
> diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> index 4e3c29bb603c..fd5dd9d278b5 100644
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -693,7 +693,9 @@ int handle_domain_irq(struct irq_domain *domain,
>  	struct irq_desc *desc;
>  	int ret = 0;
>  
> +#ifndef CONFIG_HAVE_ARCH_IRQENTRY
>  	irq_enter();
> +#endif

nit: I tend to prefer the 'if (!IS_ENABLED(CONFIG_*))' approach.

>  
>  	/* The irqdomain code provides boundary checks */
>  	desc = irq_resolve_mapping(domain, hwirq);
> @@ -702,7 +704,9 @@ int handle_domain_irq(struct irq_domain *domain,
>  	else
>  		ret = -EINVAL;
>  
> +#ifndef CONFIG_HAVE_ARCH_IRQENTRY
>  	irq_exit();
> +#endif
>  	set_irq_regs(old_regs);
>  	return ret;
>  }

Apart from that:

Reviewed-by: Marc Zyngier <maz@...nel.org>

Thanks,

	M.

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