[PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace() methods

[Peter Zijlstra]

On Wed, Mar 16, 2016 at 01:02:10PM -0400, 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 either the old "all/all_but_self" arch methods, or the new
> "cpumask" method, depending on which is available.
> 
> The existing clients of nmi_backtrace (arm and x86) are converted
> to using the new cpumask approach in this change.

So the past days I've been staring at RCU stall warns, and they can use
a little of this. Their remote stack unwinds are less than useful.