linux-kernel - Re: [PATCH v1 1/2] arm64: run softirqs on the per-CPU IRQ stack

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Date:   Fri, 22 Jul 2022 10:04:41 +0100
From:   Will Deacon <will@...nel.org>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     arnd@...db.de, catalin.marinas@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] arm64: run softirqs on the per-CPU IRQ stack

On Fri, Jul 08, 2022 at 05:49:49PM +0800, Qi Zheng 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@...edance.com>
> ---
>  arch/arm64/Kconfig      |  1 +
>  arch/arm64/kernel/irq.c | 13 +++++++++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 4c1e1d2d2f8b..be0a9f0052ee 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -230,6 +230,7 @@ config ARM64
>  	select HAVE_ARCH_USERFAULTFD_MINOR if USERFAULTFD
>  	select TRACE_IRQFLAGS_SUPPORT
>  	select TRACE_IRQFLAGS_NMI_SUPPORT
> +	select HAVE_SOFTIRQ_ON_OWN_STACK
>  	help
>  	  ARM 64-bit (AArch64) Linux support.
>  
> diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
> index bda49430c9ea..c36ad20a52f3 100644
> --- a/arch/arm64/kernel/irq.c
> +++ b/arch/arm64/kernel/irq.c
> @@ -22,6 +22,7 @@
>  #include <linux/vmalloc.h>
>  #include <asm/daifflags.h>
>  #include <asm/vmap_stack.h>
> +#include <asm/exception.h>
>  
>  /* Only access this in an NMI enter/exit */
>  DEFINE_PER_CPU(struct nmi_ctx, nmi_contexts);
> @@ -71,6 +72,18 @@ static void init_irq_stacks(void)
>  }
>  #endif
>  
> +#ifndef CONFIG_PREEMPT_RT
> +static void ____do_softirq(struct pt_regs *regs)
> +{
> +	__do_softirq();
> +}
> +
> +void do_softirq_own_stack(void)
> +{
> +	call_on_irq_stack(NULL, ____do_softirq);
> +}
> +#endif

Acked-by: Will Deacon <will@...nel.org>

Please can you repost this at -rc1 and we can queue it up for 5.21?

Thanks,

Will