linux-kernel - Re: [PATCH] arm64: secondary_start_kernel: Remove unnecessary barrier

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Date:	Tue, 10 May 2016 11:34:01 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Suzuki K Poulose <suzuki.poulose@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Will Deacon <will.deacon@....com>,
	Dennis Chen <dennis.chen@....com>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH] arm64: secondary_start_kernel: Remove unnecessary barrier

On Tue, May 10, 2016 at 11:14:41AM +0100, Suzuki K Poulose wrote:
> Remove the unnecessary smp_wmb(), which was added to make sure
> that the update_cpu_boot_status() completes before we mark the
> CPU online. But update_cpu_boot_status() already has dsb() (required
> for the failing CPUs) to ensure the correct behavior.
> 
> Cc: Will Deacon <will.deacon@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Dennis Chen <dennis.chen@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>

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

Mark.

> ---
>  arch/arm64/kernel/smp.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index b2d5f4e..ec040a8 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -225,8 +225,6 @@ asmlinkage void secondary_start_kernel(void)
>  	pr_info("CPU%u: Booted secondary processor [%08x]\n",
>  					 cpu, read_cpuid_id());
>  	update_cpu_boot_status(CPU_BOOT_SUCCESS);
> -	/* Make sure the status update is visible before we complete */
> -	smp_wmb();
>  	set_cpu_online(cpu, true);
>  	complete(&cpu_running);
>  
> -- 
> 1.7.9.5
>