Re: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked()

From: Paul E. McKenney
Date: Tue Apr 03 2018 - 10:16:38 EST

On Tue, Apr 03, 2018 at 02:52:33PM +0100, David Howells wrote:
> Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > It's more complicated than that. This function is dangerous and should be
> > > used with extreme care. In the case where CONFIG_SMP=n the value is locked
> > > one way or the other and it might be the wrong way.
> >
> > You mean "unlocked"? (aka, return 0)
> No, I mean "fixed", sorry. We've had problems stemming from this before on UP
> systems.

Oooh... I had forgotten about spinlocks disappearing on UP systems,
good catch!

Suggestions for a fix? Clearly great care is required when using it
in things like WARN_ON()...

Thanx, Paul