linux-kernel - Re: [PATCH v2 6/7] sparc/leon: Remove on-stack cpumask var

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Date: Sat, 20 Apr 2024 10:32:02 +0200
From: Sam Ravnborg <sam@...nborg.org>
To: Dawei Li <dawei.li@...ngroup.cn>
Cc: davem@...emloft.net, andreas@...sler.com, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/7] sparc/leon: Remove on-stack cpumask var

On Sat, Apr 20, 2024 at 01:15:46PM +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_subset() and cpumask_first_and() to avoid the need for a
> temporary cpumask on the stack.
> 
> Signed-off-by: Dawei Li <dawei.li@...ngroup.cn>
> ---
>  arch/sparc/kernel/leon_kernel.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/sparc/kernel/leon_kernel.c b/arch/sparc/kernel/leon_kernel.c
> index 4c61da491fee..0070655041bb 100644
> --- a/arch/sparc/kernel/leon_kernel.c
> +++ b/arch/sparc/kernel/leon_kernel.c
> @@ -106,13 +106,10 @@ unsigned long leon_get_irqmask(unsigned int irq)
>  #ifdef CONFIG_SMP
>  static int irq_choose_cpu(const struct cpumask *affinity)
>  {
> -	cpumask_t mask;
> +	unsigned int cpu = cpumask_first_and(affinity, cpu_online_mask);
>  
> -	cpumask_and(&mask, cpu_online_mask, affinity);
> -	if (cpumask_equal(&mask, cpu_online_mask) || cpumask_empty(&mask))
> -		return boot_cpu_id;
> -	else
> -		return cpumask_first(&mask);
> +	return cpumask_subset(cpu_online_mask, affinity) || cpu >= nr_cpu_ids ?
> +	       boot_cpu_id : cpu;

This looks wrong - or if it is correct is is hard to parse.
Drop ?: and use an if so the code is more readable.

	Sam