[PATCH 5/8] nvme: sync the namespace scanning during ctrl start

[Sagi Grimberg]

>>>>> @@ -4537,9 +4536,10 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
>>>>>           nvme_change_uevent(ctrl, "NVME_EVENT=rediscover");
>>>>>       if (ctrl->queue_count > 1) {
>>>>> -        nvme_queue_scan(ctrl);
>>>>> +        nvme_queue_scan_sync(ctrl);
>>>>>           nvme_unquiesce_io_queues(ctrl);
>>>>>           nvme_mpath_update(ctrl);
>>>>> +        nvme_kick_requeue_lists(ctrl);
>>>>>       }
>>>>
>>>> I really don't think its a good idea to block ctrl start
>>>> like that.
>>>
>>> like how ? scan_sync ?
>>
>> Yes
> 
> why not ? this is control path..

Because in the real world, namespaces (or HCAs) will not change their
attributes in 99.999999% of the cases, and when they do, in 99.999999%
of the cases the inflight IO has already failed over to a different
path.

So no, I don't think that preventing the ctrl start from making forward
progress until a full namespaces scan completes makes any sense.

> we have to make sure we issue commands to a validated namespace.

I think we should simply refuse to create the ns when it differs between
paths, or remove it in the highly unlikely case where it suddenly
changes its attributes when reconnecting.