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

[Christoph Hellwig]

On Mon, May 17, 2021 at 11:20:36AM -0700, Sagi Grimberg wrote:
>
>>> 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.

We also check for the matching identifiers in nvme_init_ns_head, so
we'll error out there.