[PATCH] nvme: fix namespace removal list

[Paul E. McKenney]

On Tue, Jun 11, 2024 at 10:40:13PM +0530, Nilay Shroff wrote:
> 
> 
> On 6/11/24 22:09, Christoph Hellwig wrote:
> > On Tue, Jun 11, 2024 at 08:20:55AM -0700, Keith Busch wrote:
> >>  	mutex_lock(&ctrl->namespaces_lock);
> >>  	list_for_each_entry_safe(ns, next, &ctrl->namespaces, list) {
> >> -		if (ns->head->ns_id > nsid)
> >> -			list_splice_init_rcu(&ns->list, &rm_list,
> >> -					     synchronize_rcu);
> >> +		if (ns->head->ns_id > nsid) {
> >> +			list_del_rcu(&ns->list);
> >> +			list_add_tail_rcu(&ns->list, &rm_list);
> >> +		}
> > 
> > Is this actually valid for a (S)RCU protected list?  If the entry gets
> > added to the new list before the grace period has completed, we could
> > trick a concurrent traversal into following the new list unless I'm
> > mistaken (although chances I'm mistaken on RCU corner cases aren't that
> > low..).
> > 
> > 
> I think we need synchronize_srcu() before we add deleted ns to rm_list.

After we delete it, but yes.

There will also be a window during which the element is not in either
list, but given the name "rm_list", I am guessing that this is OK.  ;-)

							Thanx, Paul