Re: [PATCH v4 01/27] lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions

Joel Fernandes
2020-02-25T02:12:22Z

On Mon, Feb 24, 2020 at 11:10:50AM +0100, Peter Zijlstra wrote:
> On Fri, Feb 21, 2020 at 10:08:43PM -0500, Joel Fernandes wrote:
> > On Fri, Feb 21, 2020 at 02:34:17PM +0100, Peter Zijlstra wrote:
> > > nmi_enter() does lockdep_off() and hence lockdep ignores everything.
> > >
> > > And NMI context makes it impossible to do full IN-NMI tracking like we
> > > do IN-HARDIRQ, that could result in graph_lock recursion.
> >
> > The patch makes sense to me.
> >
> > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> >
> > NOTE:
> > Also, I was wondering if we can detect the graph_lock recursion case and
> > avoid doing anything bad, that way we enable more of the lockdep
> > functionality for NMI where possible. Not sure if the suggestion makes sense
> > though!
>
> Yeah, I considered playing trylock games, but figured I shouldn't make
> it more complicated that it needs to be.

Yes, I agree with you. Thanks.

- Joel