linux-kernel - Re: [PATCH] arm64: Fix incorrect per-cpu usage for boot CPU

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Date:	Thu, 21 Jul 2016 11:33:07 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Suzuki K Poulose <suzuki.poulose@....com>
Cc:	catalin.marinas@....com, will.deacon@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] arm64: Fix incorrect per-cpu usage for boot CPU

On Thu, Jul 21, 2016 at 11:12:55AM +0100, Suzuki K Poulose wrote:
> In smp_prepare_boot_cpu(), we invoke cpuinfo_store_boot_cpu to  store
> the cpuinfo in a per-cpu ptr, before initialising the per-cpu offset for
> the boot CPU. This patch reorders the sequence to make sure we initialise
> the per-cpu offset before accessing the per-cpu area.
> 
> Commit 4b998ff1885eec ("arm64: Delay cpuinfo_store_boot_cpu") fixed the
> issue where we modified the per-cpu area even before the kernel initialises
> the per-cpu areas, but failed to wait until the boot cpu updated it's
> offset.
> 
> Fixes: commit 4b998ff1885eec ("arm64: Delay cpuinfo_store_boot_cpu")
> Cc: <stable@...r.kernel.org>
> Cc: Will Deacon <will.deacon@....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, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 62ff3c0..d242e81 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -437,9 +437,9 @@ void __init smp_cpus_done(unsigned int max_cpus)
>  
>  void __init smp_prepare_boot_cpu(void)
>  {
> +	set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
>  	cpuinfo_store_boot_cpu();
>  	save_boot_cpu_run_el();
> -	set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
>  }
>  
>  static u64 __init of_get_cpu_mpidr(struct device_node *dn)
> -- 
> 2.7.4
>