Re: [PATCH v8 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace() methods

[Chris Metcalf]

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