Re: [PATCH] arm64: panic if IRQ shadow call stack allocation fails

[Will Deacon <will@kernel.org>]

On Tue, Mar 24, 2026 at 05:15:41PM +0100, Osama Abdelkader wrote:
> diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
> index 15dedb385b9e..b32ed7ef8e00 100644
> --- a/arch/arm64/kernel/irq.c
> +++ b/arch/arm64/kernel/irq.c
> @@ -14,6 +14,7 @@
>  #include <linux/init.h>
>  #include <linux/irq.h>
>  #include <linux/irqchip.h>
> +#include <linux/kernel.h>
>  #include <linux/kprobes.h>
>  #include <linux/memory.h>
>  #include <linux/scs.h>
> @@ -32,23 +33,26 @@ DEFINE_PER_CPU(struct nmi_ctx, nmi_contexts);
>  
>  DEFINE_PER_CPU(unsigned long *, irq_stack_ptr);
>  
> -
>  DECLARE_PER_CPU(unsigned long *, irq_shadow_call_stack_ptr);
>  
>  #ifdef CONFIG_SHADOW_CALL_STACK
>  DEFINE_PER_CPU(unsigned long *, irq_shadow_call_stack_ptr);
>  #endif
>  
> -static void init_irq_scs(void)
> +static void __init init_irq_scs(void)
>  {
>  	int cpu;
> +	void *s;
>  
>  	if (!scs_is_enabled())
>  		return;
>  
> -	for_each_possible_cpu(cpu)
> -		per_cpu(irq_shadow_call_stack_ptr, cpu) =
> -			scs_alloc(early_cpu_to_node(cpu));
> +	for_each_possible_cpu(cpu) {
> +		s = scs_alloc(early_cpu_to_node(cpu));
> +		if (!s)
> +			panic("irq: Failed to allocate shadow call stack\n");
> +		per_cpu(irq_shadow_call_stack_ptr, cpu) = s;
> +	}

I don't especially see the point in these panic() messages given that
presumably all sorts of other things will go wrong if we fail simple
allocations this early during boot.

If you really want to check this, then we should at least do the same
for the IRQ stack itself, otherwise it's all a bit academic. So maybe
have init_irq_scs() and init_irq_stacks() return -ENOMEM so that
init_IRQ() can panic?

Will