linux-kernel - Re: [PATCH v2 6/7] irqchip/sifive-plic: Avoid explicit cpumask allocation on stack

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Date: Wed, 17 Apr 2024 16:51:00 +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 6/7] irqchip/sifive-plic: 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-sifive-plic.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
> index f3d4cb9e34f7..8fb183ced1e7 100644
> --- a/drivers/irqchip/irq-sifive-plic.c
> +++ b/drivers/irqchip/irq-sifive-plic.c
> @@ -164,15 +164,12 @@ static int plic_set_affinity(struct irq_data *d,
>                              const struct cpumask *mask_val, bool force)
>  {
>         unsigned int cpu;
> -       struct cpumask amask;
>         struct plic_priv *priv = irq_data_get_irq_chip_data(d);
>
> -       cpumask_and(&amask, &priv->lmask, mask_val);
> -
>         if (force)
> -               cpu = cpumask_first(&amask);
> +               cpu = cpumask_first_and(&priv->lmask, mask_val);
>         else
> -               cpu = cpumask_any_and(&amask, cpu_online_mask);
> +               cpu = cpumask_first_and_and(&priv->lmask, mask_val, cpu_online_mask);
>
>         if (cpu >= nr_cpu_ids)
>                 return -EINVAL;
> --
> 2.27.0
>