RE: [PATCH] smp: Do not warn if smp_call_function_single() is doing a self call.

[Dexuan Cui]

> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Sent: Monday, April 15, 2019 5:21 AM
> To: Dexuan Cui <decui@xxxxxxxxxxxxx>
> 
> On Fri, Apr 12, 2019 at 11:53:57PM +0000, Dexuan Cui wrote:
> > If smp_call_function_single() is calling the function for itself, it's safe
> > to run with irqs_disabled() == true.
> >
> > I hit the warning because I'm in the below path in the .suspend callback of
> > a "syscore_ops" to support hibernation for a VM running on Hyper-V:
> >
> >   hv_synic_cleanup() ->
> >     clockevents_unbind_device() ->
> >       clockevents_unbind() ->
> >         smp_call_function_single().
> >
> > When the .suspend callback runs, only CPU0 is online and irqs_disabled() is
> > true.
> 
> Pray tell, how well do you think mutex_lock() works with interrupts
> disabled?

Good point. I realized generally speaking this patch makes no sense, so let me
try the solution proposed by Vitaly, i.e. fix clockevents_unbind() instead.

Thanks,
-- Dexuan