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

From: Mikulas Patocka
Date: Tue Nov 21 2017 - 14:56:52 EST

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.