Re: [PATCH PREEMPT RT] rt-mutex: fix deadlock in device mapper

[Mikulas Patocka]

On Tue, 21 Nov 2017, Mike Galbraith wrote:

> On Tue, 2017-11-21 at 11:11 -0500, Mikulas Patocka wrote:
> > 
> > So, drop the spinlock unplugging and leave only mutex unplugging, 
> > reproduce the deadlock and send the stacktraces.
> 
> Nah, I reproduced it five years ago.  Is any of that relevant today?
>  Damned if I know.  Your report was the first I've noticed since.
> 
> 	-Mike

If we don't have any reason why it is needed to unplug block requests when 
a spinlock is taken - so let's not do this.

If you add code to the spinlock path and you don't know why, it is cargo 
cult programming.

Mikulas