Re: [RFC-PATCH 2/2] nvme: use the namespace id for block device names

[Keith Busch <kbusch@kernel.org>]

On Tue, Mar 03, 2026 at 08:39:56AM -0700, Keith Busch wrote:
> On Tue, Mar 03, 2026 at 08:34:38AM +0100, Hannes Reinecke wrote:
> > The idea is nice, and I would love to go into that
> > direction.
> > But have you checked how this holds up under
> > rescan/remapping (eg things like blktest/nvme/058)?
> > Removal of the sysfs nodes might be delayed, and we cannot
> > create new entries with the same name until then.
> > So if that is taken care of, fine, but I don't see that in
> > the patch ...
> 
> I see. I set out to ensure everything was ordered, but apparently I've
> missed this case. Thanks for pointing out the test.

Okay, I think it's as simple as the head unlinking prior to actually
doing the del_gendisk creates a time when one scan work makes a new
namespace before the stale one is deleted in a different scan. This
should fix it:

---
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 3f2f9b2be87c2..e8dbb6cb85694 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -4246,11 +4246,8 @@ static void nvme_ns_remove(struct nvme_ns *ns)

 	mutex_lock(&ns->ctrl->subsys->lock);
 	list_del_rcu(&ns->siblings);
-	if (list_empty(&ns->head->list)) {
-		if (!nvme_mpath_queue_if_no_path(ns->head))
-			list_del_init(&ns->head->entry);
+	if (list_empty(&ns->head->list))
 		last_path = true;
-	}
 	mutex_unlock(&ns->ctrl->subsys->lock);
 
 	/* guarantee not available in head->list */
--

This opens a different race where Controller A is deleting the last
path, and Controller B is bringing up a new namespace that reused the
NSID. An earlier patch from me should fix that by reschudeling B's
scan_work once A detects it removed the last path. It should work, but
it feels a bit off to me, so I'll think about it a little more.