linux-kernel - Re: [PATCH] ARM:kexec:offline panic_smp_self

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Date:   Thu, 1 Nov 2018 11:34:30 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Wang Yufen <wangyufen@...wei.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, kstewart@...uxfoundation.org,
        rppt@...ux.vnet.ibm.com, gregkh@...uxfoundation.org,
        tglx@...utronix.de, pombredanne@...b.com, weiyongjun1@...wei.com,
        huawei.libin@...wei.com
Subject: Re: [PATCH] ARM:kexec:offline panic_smp_self_stop CPU

On Thu, Nov 01, 2018 at 07:20:49PM +0800, Wang Yufen wrote:
> From: Yufen Wang <wangyufen@...wei.com>
> 
> In case panic() and panic() called at the same time on different CPUS.
> For example:
> CPU 0:
>   panic()
>      __crash_kexec
>        machine_crash_shutdown
>          crash_smp_send_stop
>        machine_kexec
>          BUG_ON(num_online_cpus() > 1);
> 
> CPU 1:
>   panic()
>     local_irq_disable
>     panic_smp_self_stop
> 
> If CPU 1 calls panic_smp_self_stop() before crash_smp_send_stop(), kdump
> fails. CPU1 can't receive the ipi irq, CPU1 will be always online.
> I changed BUG_ON to WARN in kexec crash as arm64 does, kdump also fails.
> Because num_online_cpus() > 1, can't disable the L2 in _soft_restart.
> To fix this problem, this patch split out the panic_smp_self_stop()
> and add set_cpu_online(smp_processor_id(), false).

Thanks.

I think this may as well go into arch/arm/kernel/smp.c - it won't be
required for single-CPU systems, since there aren't "other" CPUs.

It's probably also worth a comment above the function as to why we
have this.

> 
> Signed-off-by: Yufen Wang <wangyufen@...wei.com>
> ---
>  arch/arm/kernel/setup.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 31940bd..151861f 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -602,6 +602,16 @@ static void __init smp_build_mpidr_hash(void)
>  }
>  #endif
>  
> +void panic_smp_self_stop(void)
> +{
> +	printk(KERN_DEBUG "CPU %u will stop doing anything useful since another CPU has paniced\n",
> +			smp_processor_id());
> +	set_cpu_online(smp_processor_id(), false);
> +	while (1)
> +		cpu_relax();
> +
> +}
> +
>  static void __init setup_processor(void)
>  {
>  	struct proc_info_list *list;
> -- 
> 2.7.4
> 
> 

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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