Re: [PATCH] powerpc/irq: Allow softirq to hardirq stack transition

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 30/11/2023 à 13:50, Michael Ellerman a écrit :
> Allow a transition from the softirq stack to the hardirq stack when
> handling a hardirq. Doing so means a hardirq received while deep in
> softirq processing is less likely to cause a stack overflow of the
> softirq stack.
> 
> Previously it wasn't safe to do so because irq_exit() (which initiates
> softirq processing) was called on the hardirq stack.
> 
> That was changed in commit 1b1b6a6f4cc0 ("powerpc: handle irq_enter/
> irq_exit in interrupt handler wrappers") and 1346d00e1bdf ("powerpc:
> Don't select HAVE_IRQ_EXIT_ON_IRQ_STACK").
> 
> The allowed transitions are now:
>   - process stack -> hardirq stack
>   - process stack -> softirq stack
>   - process stack -> softirq stack -> hardirq stack
> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>


Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>



> ---
>   arch/powerpc/kernel/irq.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
> index 6f7d4edaa0bc..7504ceec5c58 100644
> --- a/arch/powerpc/kernel/irq.c
> +++ b/arch/powerpc/kernel/irq.c
> @@ -284,15 +284,14 @@ static __always_inline void call_do_irq(struct pt_regs *regs, void *sp)
>   void __do_IRQ(struct pt_regs *regs)
>   {
>   	struct pt_regs *old_regs = set_irq_regs(regs);
> -	void *cursp, *irqsp, *sirqsp;
> +	void *cursp, *irqsp;
>   
>   	/* Switch to the irq stack to handle this */
>   	cursp = (void *)(current_stack_pointer & ~(THREAD_SIZE - 1));
>   	irqsp = hardirq_ctx[raw_smp_processor_id()];
> -	sirqsp = softirq_ctx[raw_smp_processor_id()];
>   
>   	/* Already there ? If not switch stack and call */
> -	if (unlikely(cursp == irqsp || cursp == sirqsp))
> +	if (unlikely(cursp == irqsp))
>   		__do_irq(regs, current_stack_pointer);
>   	else
>   		call_do_irq(regs, irqsp);