Re: [PATCH RFC] drivers/core: Replace lockdep_set_novalidate_class() with unique class keys

[Kent Overstreet]

On 2/11/23 16:51, Linus Torvalds wrote:
> On Sat, Feb 11, 2023 at 1:41 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> > @@ -2941,7 +2944,10 @@ void device_initialize(struct device *de
> >          kobject_init(&dev->kobj, &device_ktype);
> >          INIT_LIST_HEAD(&dev->dma_pools);
> >          mutex_init(&dev->mutex);
> > -       lockdep_set_novalidate_class(&dev->mutex);
> > +       if (!lockdep_static_obj(dev)) {
> > +               lockdep_register_key(&dev->mutex_key);
> > +               lockdep_set_class(&dev->mutex, &dev->mutex_key);
> > +       }
> >          spin_lock_init(&dev->devres_lock);
> >          INIT_LIST_HEAD(&dev->devres_head);
> >          device_pm_init(dev);
>
> So I think this is the right thing to do, but I note that while that
> lockdep_set_novalidate_class() was "documented" to only be for
> 'dev->mutex' by scripts/checkpatch.pl, that horrific thing is also
> used by md/bcache/btree.c for the mca_bucket_alloc().
>
> Can we *please* get rid of it there too (it was added by the initial
> code, and never had any explicit excuse for it), possibly by using the
> same model.
>
> And then we could get rid of lockdep_set_novalidate_class() entirely.
> That would be a good thing.

Yeah, what bcache really needs (and presumably dev->mutex as well) is 
just to disable lockdep checking for self-deadlock of that lock type, 
since it's got its own deadlock avoidance and the subclass thing isn't 
good enough.

I've got a patch that should do what we want, replying from my other 
account with it.