linux-kernel - Re: [PATCH v8 1/4] nmi_backtrace: add more trigger_*_cpu

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Date:   Fri, 19 Aug 2016 21:54:31 -0400
From:   Chris Metcalf <cmetcalf@...lanox.com>
To:     Petr Mladek <pmladek@...e.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Aaron Tomlin <atomlin@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...l.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        "Ralf Baechle ralf @ linux-mips . org David S. Miller" 
        <davem@...emloft.net>, <linux-mips@...ux-mips.org>,
        <sparclinux@...r.kernel.org>, <x86@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()
 methods

On 8/18/2016 10:12 AM, Petr Mladek wrote:
> On Tue 2016-08-16 15:50:21, Chris Metcalf wrote:
>> Currently you can only request a backtrace of either all cpus, or
>> all cpus but yourself.  It can also be helpful to request a remote
>> backtrace of a single cpu, and since we want that, the logical
>> extension is to support a cpumask as the underlying primitive.
>>
>> This change modifies the existing lib/nmi_backtrace.c code to take
>> a cpumask as its basic primitive, and modifies the linux/nmi.h code
>> to use the new "cpumask" method instead.
>>
>> The mips code ignored the "include_self" boolean but with this change
>> it will now also dump a local backtrace if requested.
>>
>> diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
>> index 7429ad09fbe3..fea1fa7726e3 100644
>> --- a/arch/mips/kernel/process.c
>> +++ b/arch/mips/kernel/process.c
>> @@ -569,9 +569,16 @@ static void arch_dump_stack(void *info)
>>   	dump_stack();
>>   }
>>   
>> -void arch_trigger_all_cpu_backtrace(bool include_self)
>> +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
>>   {
>> -	smp_call_function(arch_dump_stack, NULL, 1);
>> +	long this_cpu = get_cpu();
>> +
>> +	if (cpumask_test_cpu(this_cpu, mask) && !exclude_self)
>> +		dump_stack();
> The bit is not cleared in the mask. Therefore arch_dump_stack
> will get called for this CPU as well.

Actually, and kind of confusingly, smp_call_function_many() never calls
the current cpu, even if it is in the mask.  So this code is OK as-is.

> Otherwise the patch patch looks good to me.

Great, thanks!  Should I add your Reviewed-by?

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com