Re: [PATCH 2/3] arm: introduce IRQ stacks

[Arnd Bergmann]

(also resending this reply from @kernel.org)

On Fri, Oct 16, 2020 at 12:19 PM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Thu, Oct 8, 2020 at 9:20 AM Maninder Singh <maninder1.s@xxxxxxxxxxx> wrote:
> >
> > This patch adds code for switching to IRQ stack.
> > IRQ stack and Kernel SVC stack have below design.
> >
> > IRQ STACK:-
> >                     ------------ IRQ stack top
> >                     |          |
> >                     ------------
> >                     .          .
> >                     .          .
> >                     .          .
> >                     ------------
> >                     |    sp    | <- irq_stack_base + 0x8
> >                     ------------
> >                     |    fp    | <- irq_stack_base + 0x4
> >                     ------------
> >                     |tinfo_ptr | /* pointer to thread info */
> > irq_stack_ptr -->   ------------ IRQ stack base
> >
> > Kernel SVC stack:-
> >                     ------------  Kernel stack top
> >                     |          |
> >                     ------------
> >                     .          .
> >                     .          .
> >                     .          .
> >                     ------------
> >                     |          |
> >                     |          |
> >                     ------------
> >                     |tinfo_ptr |  /* pointer to thread info */
> >                     ------------ Kernel stack base
>
> The extra indirection doesn't look great, and I don't see any of the
> other architectures need that. Since we can access percpu data
> without going through thread_info, maybe doing the same as
> x86 would work here:
>
> - define 'current' as 'this_cpu_read_stable(current_task);'
> - convert to CONFIG_THREAD_INFO_IN_TASK
>
>        Arnd