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Subject: Re: [PATCH] arm64: add dump_stack to show_regs
To: Mark Rutland <mark.rutland@arm.com>,
        Ding Tianhong <dingtianhong@huawei.com>
References: <e84a5cf9-f4c4-2b27-ed59-363e2f8ab5bc@huawei.com>
 <20170320110216.GB18585@leverpostej>
CC: Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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From: Kefeng Wang <wangkefeng.wang@huawei.com>
Message-ID: <ad975a0a-8888-3255-3ed1-117e75fd7109@huawei.com>
Date: Mon, 20 Mar 2017 21:05:04 +0800
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On 2017/3/20 19:02, Mark Rutland wrote:
> On Sun, Mar 19, 2017 at 03:15:25PM +0800, Ding Tianhong wrote:
>> Recently I found that when the system trigger a soft lockup in interrupt,
>> there is only showing the regs, but no stack trace, it is very difficult
>> to locate the problem:
>>
>> ===========================================
>>
>> [10072.999437] NMI watchdog: BUG: soft lockup - CPU#16 stuck for 23s! [ksoftirqd/16:88]
>> .....
>> [10073.041254] CPU: 16 PID: 88 Comm: ksoftirqd/16 Tainted: G         4.x.x #1
>> [10073.041258] Hardware name: xxxxx, BIOS 1.17 01/04/2017
>> [10073.041261] task: ffff803f6cb06200 ti: ffff803f6cb50000 task.ti: ffff803f6cb50000
>> [10073.041274] PC is at _raw_spin_unlock_irqrestore+0x24/0x30
>> [10073.041280] LR is at blk_run_queue+0x3c/0x48
>> [10073.041282] pc : [<ffff800000a3df14>] lr : [<ffff8000004f3a7c>] pstate: 60000145
>> [10073.041285] sp : ffff803f6cb53b20
>> [10073.041286] x29: ffff803f6cb53b20 x28: 0000000000001000
>> [10073.041290] x27: 0000000000000000 x26: ffff800001226000
>> [10073.041294] x25: 0000000000000000 x24: 0000000000000140
>> [10073.041297] x23: ffff803f62e108c8 x22: ffff800001037000
>> [10073.041302] x21: ffff843f66800040 x20: 0000000000000140
>> [10073.041305] x19: ffff803f62e108c8 x18: 0000000000000007
>> [10073.041309] x17: 000000000000000e x16: 0000000000000001
>> [10073.041312] x15: 0000000000000019 x14: 0000000000000033
>> [10073.041317] x13: 000000000000004c x12: 0000000000000000
>> [10073.041320] x11: 0000000000001000 x10: 0000000000000010
>> [10073.041323] x9 : ffff8000004f3a7c x8 : ffff803f69b59120
>> [10073.041327] x7 : 0000000000000000 x6 : 0000000000000002
>> [10073.041331] x5 : 0000000000000244 x4 : 00000000000244d9
>> [10073.041334] x3 : ffff843f653ab918 x2 : 0000000000004074
>> [10073.041337] x1 : 0000000000000140 x0 : ffff803f62e10e58
>>
>> ===============================================
>>
>> So add the general dump_stack to show_regs to support showing the stack.
>>
>> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
>> ---
>>  arch/arm64/kernel/process.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
>> index 043d373..60c5c26 100644
>> --- a/arch/arm64/kernel/process.c
>> +++ b/arch/arm64/kernel/process.c
>> @@ -212,6 +212,7 @@ void show_regs(struct pt_regs * regs)
>>  {
>>  	printk("\n");
>>  	__show_regs(regs);
>> +	dump_stack();
>>  }
> 
> I don't think this is quite right.

I found the same logic exists in arm32.

> 
> I see that x86's show_regs() will dump a kernel stack, but it starts
> from the stack described by the regs, not the stack used to call
> dump_stack().
> 
> Also, for longjmp_break_handler() I think we only want the current
> registers, and not the stack.

Is there a better way to show the kernel stack? it is not early to address issue
if only show regs. Making a new show_regs() to call dump_mem()/dump_backtrace()/dump_instr()?

Thanks,
Kefeng

> 
> Thanks,
> Mark.
> 
> _______________________________________________
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> 
> .
>