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

Peter Zijlstra
2020-02-24T10:11:22Z

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.