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

On 3/15/2021 10:08 PM, Sagi Grimberg wrote:

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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/ (local) 


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.

Agree with Sagi. We also hit this issue a long time ago and I made the 
same change (commit 834d3710a093a) that Sagi is suggesting:  if the 
prior controller instance had io queues, but the new/reconnected 
controller fails to create io queues, then the controller create is 
failed and a reconnect is scheduled.

-- james



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