[PATCH 2/2] nvme: add 'queue_if_no_path' semantics

[Keith Busch]

On Tue, Oct 06, 2020 at 03:30:14PM +0200, Hannes Reinecke wrote:
> but the re-added device isn't added to the MD RAID.
> In fact, it has been assigned a _different_ namespace ID:

That's actually just a driver assigned instance rather than a Namespace
ID. 
 
> [  904.299065] pcieport 0000:00:08.0: pciehp: Slot(0-1): Card present
> [  904.299067] pcieport 0000:00:08.0: pciehp: Slot(0-1): Link Up
> [  904.435314] pci 0000:02:00.0: [8086:5845] type 00 class 0x010802
> [  904.435523] pci 0000:02:00.0: reg 0x10: [mem 0x00000000-0x00001fff 64bit]
> [  904.435676] pci 0000:02:00.0: reg 0x20: [mem 0x00000000-0x00000fff]
> [  904.436982] pci 0000:02:00.0: BAR 0: assigned [mem 0xc1200000-0xc1201fff 64bit]
> [  904.437086] pci 0000:02:00.0: BAR 4: assigned [mem 0xc1202000-0xc1202fff]
> [  904.437118] pcieport 0000:00:08.0: PCI bridge to [bus 02]
> [  904.437137] pcieport 0000:00:08.0:   bridge window [io  0x7000-0x7fff]
> [  904.439024] pcieport 0000:00:08.0:   bridge window [mem 0xc1200000-0xc13fffff]
> [  904.440229] pcieport 0000:00:08.0:   bridge window [mem 0x802000000-0x803ffffff 64bit pref]
> [  904.447150] nvme nvme3: pci function 0000:02:00.0
> [  904.447487] nvme 0000:02:00.0: enabling device (0000 -> 0002)
> [  904.458880] nvme nvme3: 1/0/0 default/read/poll queues
> [  904.461296] nvme1n2: detected capacity change from 0 to 4294967296
> 
> and the 'old', pre-hotplug device still lingers on in the 'nvme list'
> output.

I think what you're showing is a problem for everyone, including
fabrics. The namespace was attached to the previously existing
subsystem, nvme1, but we didn't find the previously existing "head" to
reattach the namespace.

I just threw the below together very hastily, so I'm sure there's
something wrong with it, but just to capture what's wrong with the
current code:

---
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 3833584b5cee..0b3bbbe6d1e8 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3897,8 +3897,6 @@ 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))
-		list_del_init(&ns->head->entry);
 	mutex_unlock(&ns->ctrl->subsys->lock);
 
 	synchronize_rcu(); /* guarantee not available in head->list */
--