[PATCHv4] nvme: allow to re-attach namespaces after all paths are down

[Sagi Grimberg]

>> That is because we keep the device node around even though it doesn't
>> have any bottom devices. Which is what I think Hannes tried to fix
>> in an earlier patch.
>>
>> Also, if an NVM subsystem happens to recycle nsids, it will trigger
>> pretty surely. So I'm not sure this is an obscure case...
> 
> I'm not very concerned because (1) deleting an in-use namespace is
> surely a user error, and (2) it currently doesn't work either, and no
> one's complained yet AFAIK.

You're not wrong. It's just that one error (on ns X) can manifest in
other potentially completely different namespaces created. I guess
this kind of thing can happen when ns administration is done by
adminX (or scriptX) and the ns mounting is done by userY where what each
is doing is unknown to each other.