linux-kernel - Re: [PATCH v2 4/7] irqchip/loongson-eiointc: Avoid explicit cpumask allocation on stack

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Message-ID: <Zh69CzD26Z4hw6R9@yury-ThinkPad>
Date: Tue, 16 Apr 2024 11:01:47 -0700
From: Yury Norov <yury.norov@...il.com>
To: Dawei Li <dawei.li@...ngroup.cn>
Cc: tglx@...utronix.de, rafael@...nel.org, akpm@...ux-foundation.org,
	maz@...nel.org, florian.fainelli@...adcom.com,
	chenhuacai@...nel.org, jiaxun.yang@...goat.com, anup@...infault.org,
	palmer@...belt.com, samuel.holland@...ive.com,
	linux@...musvillemoes.dk, daniel.lezcano@...aro.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] irqchip/loongson-eiointc: Avoid explicit cpumask
 allocation on stack

On Tue, Apr 16, 2024 at 04:54:51PM +0800, Dawei Li wrote:
> In general it's preferable to avoid placing cpumasks on the stack, as
> for large values of NR_CPUS these can consume significant amounts of
> stack space and make stack overflows more likely.
> 
> Use cpumask_first_and_and() to avoid the need for a temporary cpumask on
> the stack.
> 
> Signed-off-by: Dawei Li <dawei.li@...ngroup.cn>
> ---
>  drivers/irqchip/irq-loongson-eiointc.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-loongson-eiointc.c b/drivers/irqchip/irq-loongson-eiointc.c
> index 4f5e6d21d77d..c7ddebf312ad 100644
> --- a/drivers/irqchip/irq-loongson-eiointc.c
> +++ b/drivers/irqchip/irq-loongson-eiointc.c
> @@ -93,19 +93,15 @@ static int eiointc_set_irq_affinity(struct irq_data *d, const struct cpumask *af
>  	unsigned int cpu;
>  	unsigned long flags;
>  	uint32_t vector, regaddr;
> -	struct cpumask intersect_affinity;
>  	struct eiointc_priv *priv = d->domain->host_data;
>  
>  	raw_spin_lock_irqsave(&affinity_lock, flags);
>  
> -	cpumask_and(&intersect_affinity, affinity, cpu_online_mask);
> -	cpumask_and(&intersect_affinity, &intersect_affinity, &priv->cpuspan_map);
> -
> -	if (cpumask_empty(&intersect_affinity)) {

This was unneeded because cpumask_and() returns true if there are set
bits.

For the series:

Reviewed-by: Yury Norov <yury.norov@...il.com>

> +	cpu = cpumask_first_and_and(&priv->cpuspan_map, affinity, cpu_online_mask);
> +	if (cpu >= nr_cpu_ids) {
>  		raw_spin_unlock_irqrestore(&affinity_lock, flags);
>  		return -EINVAL;
>  	}
> -	cpu = cpumask_first(&intersect_affinity);
>  
>  	vector = d->hwirq;
>  	regaddr = EIOINTC_REG_ENABLE + ((vector >> 5) << 2);
> -- 
> 2.27.0