linux-kernel - Re: [PATCH v2 5/7] irqchip/riscv-aplic-direct: Avoid explicit cpumask allocation on stack

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Date: Wed, 17 Apr 2024 16:52:00 +0530
From: Anup Patel <anup@...infault.org>
To: Dawei Li <dawei.li@...ngroup.cn>
Cc: tglx@...utronix.de, yury.norov@...il.com, rafael@...nel.org, 
	akpm@...ux-foundation.org, maz@...nel.org, florian.fainelli@...adcom.com, 
	chenhuacai@...nel.org, jiaxun.yang@...goat.com, palmer@...belt.com, 
	samuel.holland@...ive.com, linux@...musvillemoes.dk, 
	daniel.lezcano@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/7] irqchip/riscv-aplic-direct: Avoid explicit cpumask
 allocation on stack

On Tue, Apr 16, 2024 at 2:26 PM Dawei Li <dawei.li@...ngroup.cn> 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>

LGTM.

Reviewed-by: Anup Patel <anup@...infault.org>

Regards,
Anup

> ---
>  drivers/irqchip/irq-riscv-aplic-direct.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/irqchip/irq-riscv-aplic-direct.c b/drivers/irqchip/irq-riscv-aplic-direct.c
> index 06bace9b7497..4a3ffe856d6c 100644
> --- a/drivers/irqchip/irq-riscv-aplic-direct.c
> +++ b/drivers/irqchip/irq-riscv-aplic-direct.c
> @@ -54,15 +54,12 @@ static int aplic_direct_set_affinity(struct irq_data *d, const struct cpumask *m
>         struct aplic_direct *direct = container_of(priv, struct aplic_direct, priv);
>         struct aplic_idc *idc;
>         unsigned int cpu, val;
> -       struct cpumask amask;
>         void __iomem *target;
>
> -       cpumask_and(&amask, &direct->lmask, mask_val);
> -
>         if (force)
> -               cpu = cpumask_first(&amask);
> +               cpu = cpumask_first_and(&direct->lmask, mask_val);
>         else
> -               cpu = cpumask_any_and(&amask, cpu_online_mask);
> +               cpu = cpumask_first_and_and(&direct->lmask, mask_val, cpu_online_mask);
>
>         if (cpu >= nr_cpu_ids)
>                 return -EINVAL;
> --
> 2.27.0
>