linux-kernel - Re: [PATCH V4 6/8] riscv: Support HAVE_IRQ_EXIT_ON_IRQ

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Date:   Thu, 8 Sep 2022 18:08:23 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     guoren@...nel.org
Cc:     arnd@...db.de, palmer@...osinc.com, tglx@...utronix.de,
        peterz@...radead.org, luto@...nel.org, conor.dooley@...rochip.com,
        heiko@...ech.de, jszhang@...nel.org, lazyparser@...il.com,
        falcon@...ylab.org, chenhuacai@...nel.org, apatel@...tanamicro.com,
        atishp@...shpatra.org, palmer@...belt.com,
        paul.walmsley@...ive.com, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V4 6/8] riscv: Support HAVE_IRQ_EXIT_ON_IRQ_STACK

On 2022-09-07 22:25:04 [-0400], guoren@...nel.org wrote:
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index a07bb3b73b5b..a8a12b4ba1a9 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -433,6 +433,14 @@ config FPU
>  
>  	  If you don't know what to do here, say Y.
>  
> +config IRQ_STACKS
> +	bool "Independent irq stacks"
> +	default y
> +	select HAVE_IRQ_EXIT_ON_IRQ_STACK
> +	help
> +	  Add independent irq stacks for percpu to prevent kernel stack overflows.
> +	  We may save some memory footprint by disabling IRQ_STACKS.

Do you really think that it is needed to save memory here? Avoiding
stack overflows in deep call chains is probably more important than
saving ~8KiB per CPU.

Sebastian