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

[Osama Abdelkader <osama.abdelkader@gmail.com>]

On Wed, Mar 25, 2026 at 04:35:35PM +0000, Will Deacon wrote:
> 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

Thanks for the review, I just did that in v2:
[PATCH v2] arm64: panic from init_IRQ if IRQ handler stacks cannot be
 allocated

Best regards,
Osama