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

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Date:   Mon, 22 Aug 2016 10:33:42 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Chris Metcalf <cmetcalf@...lanox.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 Fri 2016-08-19 21:54:31, Chris Metcalf wrote:
> 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.

I see it now.

> >Otherwise the patch patch looks good to me.
> 
> Great, thanks!  Should I add your Reviewed-by?

Yup. This patch looks fine then:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr