linux-kernel - Re: [PATCH v3 6/6] irqchip: sifive-plic: Implement irq_set

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Date:   Mon, 17 Dec 2018 10:32:20 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Anup Patel <anup@...infault.org>
Cc:     Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Atish Patra <atish.patra@....com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 6/6] irqchip: sifive-plic: Implement
 irq_set_affinity() for SMP host

On Fri, Nov 30, 2018 at 01:32:07PM +0530, Anup Patel wrote:
> This patch provides irq_set_affinity() implementation for PLIC driver.
> It also updates irq_enable() such that PLIC interrupts are only enabled
> for one of CPUs specified in IRQ affinity mask.

But normally our affinity masks are that - masks of CPUs that can take
it.  It seems a bit odd to then just pick the first one, as this means
with default all-CPU masks we'll have all interrupts handled by the
first CPU only.


> --- a/drivers/irqchip/irq-sifive-plic.c
> +++ b/drivers/irqchip/irq-sifive-plic.c
> @@ -106,14 +106,42 @@ static void plic_irq_toggle(const struct cpumask *mask, int hwirq, int enable)
>  
>  static void plic_irq_enable(struct irq_data *d)
>  {
> -	plic_irq_toggle(irq_data_get_affinity_mask(d), d->hwirq, 1);
> +	unsigned int cpu = cpumask_any_and(irq_data_get_affinity_mask(d),
> +					   cpu_online_mask);
> +	WARN_ON(cpu >= nr_cpu_ids);

I think this should be WARN_ON_ONCE and actually return instead of then
proceeding using the invalid cpu index. 

> +#ifdef CONFIG_SMP
static int plic_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
> +			    bool force)
> +{
> +	unsigned int cpu;
> +
> +	if (!force)
> +		cpu = cpumask_any_and(mask_val, cpu_online_mask);
> +	else
> +		cpu = cpumask_first(mask_val);

maybe swap the two branches around to avoid the inversion of the force
flag?