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Message-ID: <5dbced25-7cef-7078-78a9-f47545e6a9fe@bytedance.com>
Date:   Fri, 5 Aug 2022 15:10:34 +0800
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Subject: Re: [PATCH v2] arm64: run softirqs on the per-CPU IRQ stack
Content-Language: en-US
To:     will@kernel.org
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Mark Rutland <mark.rutland@arm.com>
References: <20220802065325.39740-1-zhengqi.arch@bytedance.com>
From:   Qi Zheng <zhengqi.arch@bytedance.com>
In-Reply-To: <20220802065325.39740-1-zhengqi.arch@bytedance.com>
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On 2022/8/2 14:53, 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@bytedance.com>
> Reviewed-by: Arnd Bergmann <arnd@arndb.de>
> Acked-by: Will Deacon <will@kernel.org>

Hi Will,

Are we good to merge it into 6.0-rc1?

Thanks,
Qi

> ---
> v1: https://lore.kernel.org/lkml/20220708094950.41944-1-zhengqi.arch@bytedance.com/
> RFC: https://lore.kernel.org/lkml/20220707110511.52129-1-zhengqi.arch@bytedance.com/
> 
> Changelog in v1 -> v2:
>   - temporarily discard [PATCH v1 2/2] to allow this patch to be merged first
>   - rebase onto the v5.19
>   - collect Reviewed-by and Acked-by
> 
> Changelog in RFC -> v1:
>   - fix conflicts with commit f2c5092190f2 ("arch/*: Disable softirq stacks on PREEMPT_RT.")
> 
>   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 1652a9800ebe..90f1ab403724 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -226,6 +226,7 @@ config ARM64
>   	select THREAD_INFO_IN_TASK
>   	select HAVE_ARCH_USERFAULTFD_MINOR if USERFAULTFD
>   	select TRACE_IRQFLAGS_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
> +
>   static void default_handle_irq(struct pt_regs *regs)
>   {
>   	panic("IRQ taken without a root IRQ handler\n");

-- 
Thanks,
Qi