[PATCH] nvme-fabrics: fix crash for no IO queues

[Sagi Grimberg]

>>>>>> A crash happens when set feature(NVME_FEAT_NUM_QUEUES) timeout in nvme
>>>>>> over rdma(roce) reconnection, the reason is use the queue which is not
>>>>>> alloced.
>>>>>>
>>>>>> If queue is not live, should not allow queue request.
>>>>>
>>>>> Can you describe exactly the scenario here? What is the state
>>>>> here? LIVE? or DELETING?
>>>> If seting feature(NVME_FEAT_NUM_QUEUES) failed due to time out or
>>>> the target return 0 io queues, nvme_set_queue_count will return 0,
>>>> and then reconnection will continue and success. The state of controller
>>>> is LIVE. The request will continue to deliver by call ->queue_rq(),
>>>> and then crash happens.
>>>
>>> Thinking about this again, we should absolutely fail the reconnection
>>> when we are unable to set any I/O queues, it is just wrong to
>>> keep this controller alive...
>> Keith think keeping the controller alive for diagnose is better.
>> This is the patch which failed the connection.
>> https://lore.kernel.org/linux-nvme/20210223072602.3196-1-lengchao@huawei.com/
>>
>> Now we have 2 choice:
>> 1.failed the connection when unable to set any I/O queues.
>> 2.do not allow queue request when queue is not live.
> 
> Okay, so there are different views on how to handles this. I personally find
> in-band administration for a misbehaving device is a good thing to have, but I
> won't 'nak' if the consensus from the people using this is for the other way.

While I understand that this can be useful, I've seen it do more harm
than good. It is really puzzling to people when the controller state
reflected is live (and even optimized) and no I/O is making progress for
unknown reason. And logs are rarely accessed in these cases.

I am also opting for failing it and rescheduling a reconnect.