RE: [PATCH 1/2] arm: traps: move declaration for irq_stack_ptr to irq.h

[Maninder Singh]

Hi Linus Walleij,

> Hi Maninder,
> 
> thanks for your patch!
> 
> On Mon, Apr 27, 2026 at 7:52 AM Maninder Singh <maninder1.s@xxxxxxxxxxx> wrote:
> 
> > Moving declaration for irq_stack_ptr to irq.h,
> > because next patch will use it for IRQ STACK checking.
> 
> OK
> 
> > Also irq_stack_ptr is defined as READ_MOSTLY, so declaration
> > should also be the same.
> 
> But is that even right in the first place?
> 
> AFAIU a stack pointer is usually read exactly as much as it
> is written.
> 

I checked for ARM64 as well, and it was "not" defined as READ_MOSTLY.
But instead of changing it, I kept it same.

Because I thought it is written during system boot only, and after that
it is read only. That might be the reason ARM has kept it as READ_MOSTLY?

arch/arm/kernel/irq.c

static void __init init_irq_stacks(void)
{
..
per_cpu(irq_stack_ptr, cpu) = &stack[THREAD_SIZE];
...
}

There is no other write to this after that I think.

stack can be read and write , but this pointer is read mostly after initial setup.

Thanks and Regards,
Maninder Singh