[PATCH V3 02/10] nvme-core: use xarray for ctrl ns tracking

[Matthew Wilcox]

On Tue, Jul 14, 2020 at 05:55:09PM -0700, Keith Busch wrote:
> On Tue, Jul 14, 2020 at 04:30:49PM -0700, Chaitanya Kulkarni wrote:
> > @@ -3933,9 +3918,7 @@ static void nvme_ns_remove(struct nvme_ns *ns)
> >  			blk_integrity_unregister(ns->disk);
> >  	}
> >  
> > -	down_write(&ns->ctrl->namespaces_rwsem);
> > -	list_del_init(&ns->list);
> > -	up_write(&ns->ctrl->namespaces_rwsem);
> > +	xa_erase(xa, ns->head->ns_id);
> 
> Since you're using rcu to protect the kref_get() on load, we need a
> synchronize_rcu() after removing it from the xarray.

No, synchronize_rcu() is expensive.  We should instead use call_rcu()
to free the ns once the refcount hits zero.