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Date:   Mon, 23 May 2022 12:34:15 +0100
From:   Mark Rutland <mark.rutland@arm.com>
To:     andrey.konovalov@linux.dev
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com,
        Catalin Marinas <catalin.marinas@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: Re: [PATCH 2/2] arm64: stacktrace: use non-atomic __set_bit
Message-ID: <YotxNzMfMdqw0uY2@FVFF77S0Q05N>
References: <697e015e22ea78b021c2546f390ad5d773f3af86.1653177005.git.andreyknvl@google.com>
 <a584e95f613d59c7ff45686c2805deb63bd61442.1653177005.git.andreyknvl@google.com>
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On Sun, May 22, 2022 at 01:50:59AM +0200, andrey.konovalov@linux.dev wrote:
> From: Andrey Konovalov <andreyknvl@google.com>
> 
> Use the non-atomic version of set_bit() in arch/arm64/kernel/stacktrace.c,
> as there is no concurrent accesses to frame->prev_type.
> 
> This speeds up stack trace collection and improves the boot time of
> Generic KASAN by 2-5%.
> 
> Suggested-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
>  arch/arm64/kernel/stacktrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 33e96ae4b15f..03593d451b0a 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -103,7 +103,7 @@ static int notrace unwind_frame(struct task_struct *tsk,
>  		if (fp <= frame->prev_fp)
>  			return -EINVAL;
>  	} else {
> -		set_bit(frame->prev_type, frame->stacks_done);
> +		__set_bit(frame->prev_type, frame->stacks_done);
>  	}
>  
>  	/*
> -- 
> 2.25.1
>