Re: [RFC PATCH 1/2] arm64: run softirqs on the per-CPU IRQ stack

[Arnd Bergmann]

On Thu, Jul 7, 2022 at 1:05 PM Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:
>
> Currently arm64 supports per-CPU IRQ stack, but softirqs
> are still handled in the task context.
>
> Since any call to local_bh_enable() at any level in the task's
> call stack may trigger a softirq processing run, which could
> potentially cause a task stack overflow if the combined stack
> footprints exceed the stack's size, let's run these softirqs
> on the IRQ stack as well.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>

I think this is the correct approach, but your patch conflicts with another
patch I have queued up in the asm-generic tree, see
https://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic.git/commit/?h=asm-generic&id=f2c5092190f21

Please adapt accordingly.

Are there any architectures left that use IRQ stacks but don't
set HAVE_SOFTIRQ_ON_OWN_STACK? If not, we could
also consider removing the Kconfig symbol and just requiring
it to be done this way (for non-PREEMPT_RT).

        Arnd