Subject: Re: Linux crashes when trying to online secondary core
From: Mason <slash.tmp@free.fr>
To: Linux ARM <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        Mark Rutland <mark.rutland@arm.com>,
        Anna-Maria Gleixner <anna-maria@linutronix.de>,
        Richard Cochran <rcochran@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Sebastian Frias <sf84@laposte.net>,
        Thibaud Cornic <thibaud_cornic@sigmadesigns.com>,
        Robin Murphy <robin.murphy@arm.com>
References: <ef972981-3fb6-74a4-cd83-a6629d2dab2a@free.fr>
 <alpine.DEB.2.20.1612141807410.3556@nanos>
 <8a021a90-e69e-f38b-c8df-ea8963f3973f@free.fr>
Message-ID: <1147ef90-7877-e4d2-bb2b-5c4fa8d3144b@free.fr>
Date: Thu, 15 Dec 2016 11:35:12 +0100
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On 14/12/2016 18:47, Mason wrote:

> On 14/12/2016 18:08, Thomas Gleixner wrote:
> 
>> On Wed, 14 Dec 2016, Mason wrote:
>>
>>> I'm seeing Linux v4.9 crash (dereferencing NULL) when I try to online
>>> the secondary core, after putting it offline.
>>
>> Does the patch below fix the issue?
>>
>> Thanks,
>>
>> 	tglx
>> 	
>> 8<---------------
>>
>> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
>> index 22acee76cf4c..2594c287b078 100644
>> --- a/include/linux/cpuhotplug.h
>> +++ b/include/linux/cpuhotplug.h
>> @@ -101,7 +101,6 @@ enum cpuhp_state {
>>  	CPUHP_AP_ARM_L2X0_STARTING,
>>  	CPUHP_AP_ARM_ARCH_TIMER_STARTING,
>>  	CPUHP_AP_ARM_GLOBAL_TIMER_STARTING,
>> -	CPUHP_AP_DUMMY_TIMER_STARTING,
>>  	CPUHP_AP_JCORE_TIMER_STARTING,
>>  	CPUHP_AP_EXYNOS4_MCT_TIMER_STARTING,
>>  	CPUHP_AP_ARM_TWD_STARTING,
>> @@ -111,6 +110,7 @@ enum cpuhp_state {
>>  	CPUHP_AP_MARCO_TIMER_STARTING,
>>  	CPUHP_AP_MIPS_GIC_TIMER_STARTING,
>>  	CPUHP_AP_ARC_TIMER_STARTING,
>> +	CPUHP_AP_DUMMY_TIMER_STARTING,
>>  	CPUHP_AP_KVM_STARTING,
>>  	CPUHP_AP_KVM_ARM_VGIC_INIT_STARTING,
>>  	CPUHP_AP_KVM_ARM_VGIC_STARTING,
> 
> $ patch -p1 < tglx.patch 
> patching file include/linux/cpuhotplug.h
> Hunk #1 succeeded at 80 (offset -21 lines).
> Hunk #2 succeeded at 89 (offset -21 lines).
> 
> It does seem to fix the problem:
> 
> # echo 0 > /sys/devices/system/cpu/cpu1/online
> SMC called with a0=0x00[000001 a1=0x00000121 a2=0x00000005  a3 =0xc01189b4  0x00000121
> [1][flow/suspend3.c:39] CPU 1 die: jumping6 to. post-boot WFE
> 402826] CPU1: shutdown
> SMC called with a0=0x00000001 a1=0x00000122 a2=0x00000000 a3=0x00000000 0x00000122
> [0][flow/suspend.c:82] Killing core1
> armor+++ armor: core 1 booted, entering wfe...
> # echo 1 > /sys/devices/system/cpu/cpu1/online
> [  215.692700] tango_boot_secondary from __cpu_up
> SMC called with a0=0x80101500 a1=0x00000105 a2=0x00000000 a3=0x00000000 0x00000105
> [  215.704494] tango_set_aux_boot_addr=0
> SMC called with a0=0x00000001 a1=0x00000104 a2=0x00000000 a3=0x00000000 0x00000104
> [0][flow/smc_handler.c:127] waking up CPU1
> [  215.719308] tango_start_aux_core=0
> 
> 
> I reverted your patch, and the kernel blows up again.
> 
> So what's the problem, and how does your patch solve it?

Link to the original report:
https://marc.info/?l=linux-arm-kernel&m=148173152524746&w=2

Forgot to CC Robin Murphy, who had provided valuable input
in similar circumstances a few months back.

Also add LKML, since this doesn't appear to be ARM-specific.

Do I need to specify which device tree I was using?

Regards.