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Subject: Re: [PATCH] ARM:kexec:offline panic_smp_self_stop CPU
To:     Russell King - ARM Linux <linux@armlinux.org.uk>
References: <1541071249-15660-1-git-send-email-wangyufen@huawei.com>
 <20181101113430.GO30658@n2100.armlinux.org.uk>
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        <kstewart@linuxfoundation.org>, <rppt@linux.vnet.ibm.com>,
        <gregkh@linuxfoundation.org>, <tglx@linutronix.de>,
        <pombredanne@nexb.com>, <weiyongjun1@huawei.com>,
        <huawei.libin@huawei.com>
From:   wangyufen <wangyufen@huawei.com>
Message-ID: <5BDBA58C.9090803@huawei.com>
Date:   Fri, 2 Nov 2018 09:17:00 +0800
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On 2018/11/1 19:34, Russell King - ARM Linux wrote:
> On Thu, Nov 01, 2018 at 07:20:49PM +0800, Wang Yufen wrote:
>> From: Yufen Wang <wangyufen@huawei.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.

Thanks.

I will send v2.

>> Signed-off-by: Yufen Wang <wangyufen@huawei.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
>>
>>