linux-kernel - Re: [PATCH] arm64: make secondary_start

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Date:   Tue, 12 Jun 2018 10:27:03 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Zhizhou Zhang <zhizhouzhang@...micro.com>, catalin.marinas@....com,
        will.deacon@....com, james.morse@....com, mark.rutland@....com,
        julien.thierry@....com, hoeun.ryu@...il.com,
        ard.biesheuvel@...aro.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: make secondary_start_kernel() notrace

On 12/06/18 10:07, Zhizhou Zhang wrote:
> We can't call function trace hook before setup percpu offset.
> When entering secondary_start_kernel(), percpu offset has not
> been initialized.  So this lead hotplug malfunction.
> Here is the flow to reproduce this bug:
> 
> echo 0 > /sys/devices/system/cpu/cpu1/online
> echo function > /sys/kernel/debug/tracing/current_tracer
> echo 1 > /sys/kernel/debug/tracing/tracing_on
> echo 1 > /sys/devices/system/cpu/cpu1/online
> 
> Signed-off-by: Zhizhou Zhang <zhizhouzhang@...micro.com>
> ---
>   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 f3e2e3ae..11b0f30 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -179,7 +179,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
>    * This is the secondary CPU boot entry.  We're using this CPUs
>    * idle thread stack, but a set of temporary page tables.
>    */
> -asmlinkage void secondary_start_kernel(void)
> +notrace asmlinkage void secondary_start_kernel(void)
>   {
>   	u64 mpidr = read_cpuid_mpidr() & MPIDR_HWID_BITMASK;
>   	struct mm_struct *mm = &init_mm;
> 

Tested-by: Suzuki K Poulose <suzuki.poulose@....com>

I think this should go to stable releases as well.

Suzuki