Re: [PATCH v3 2/8] cxl/acpi: Add root device lockdep validation

[Dan Williams]

On Mon, Apr 25, 2022 at 9:05 AM Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> On Mon, Apr 25, 2022 at 3:33 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > On Sat, Apr 23, 2022 at 10:27:52AM -0700, Dan Williams wrote:
> >
> > > ...so I'm going to drop it and just add a comment about the
> > > expectations. As Peter said there's already a multitude of ways to
> > > cause false positive / negative results with lockdep so this is just
> > > one more area where one needs to be careful and understand the lock
> > > context they might be overriding.
> >
> > One safe-guard might be to check the class you're overriding is indeed
> > __no_validate__, and WARN if not. Then the unconditional reset is
> > conistent.
> >
> > Then, if/when, that WARN ever triggers you can revisit all this.
>
> Ok, that does seem to need a dummy definition of lockdep_match_class()
> in the CONFIG_LOCKDEP=n case, but that seems worth it to me for the
> sanity check.

Thankfully the comment in lockdep.h to not define a
lockdep_match_class() for the CONFIG_LOCKDEP=n stopped me from going
that direction.