Message-ID: <88684d2f-8b36-40c4-99c8-ea07f42dd805@suse.de>
Date: Thu, 11 Apr 2024 09:11:51 +0200
From: Hannes Reinecke <hare@...e.de>
To: Sagi Grimberg <sagi@...mberg.me>, Daniel Wagner <dwagner@...e.de>
Cc: Christoph Hellwig <hch@....de>, Keith Busch <kbusch@...nel.org>,
 James Smart <james.smart@...adcom.com>, linux-nvme@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/6] nvme: authentication error are always
 non-retryable

On 4/10/24 15:50, Sagi Grimberg wrote:
> 
> 
> On 10/04/2024 15:05, Hannes Reinecke wrote:
>> On 4/10/24 12:21, Sagi Grimberg wrote:
>>>
>>>
>>> On 10/04/2024 9:52, Daniel Wagner wrote:
>>>> On Tue, Apr 09, 2024 at 11:26:00PM +0300, Sagi Grimberg wrote:
>>>>>
>>>>> On 09/04/2024 12:35, Daniel Wagner wrote:
>>>>>> From: Hannes Reinecke <hare@...e.de>
>>>>>>
>>>>>> Any authentication errors which are generated internally are always
>>>>>> non-retryable, so use negative error codes to ensure they are not
>>>>>> retried.
>>>>> The patch title says that any authentication error is not 
>>>>> retryable, and
>>>>> the patch body says "authentication errors which are generated locally
>>>>> are non-retryable" so which one is it?
>>>> Forgot to update the commit message. What about:
>>>>
>>>>    All authentication errors are non-retryable, so use negative error
>>>>    codes to ensure they are not retried.
>>>>
>>>> ?
>>>
>>> I have a question, what happens if nvmet updated its credentials (by 
>>> the admin) and in the period until the host got his credentials 
>>> updated, it
>>> happens to disconnect/reconnect. It will see an authentication
>>> error, so it will not retry and remove the controller altogether?
>>>
>>> Sounds like an issue to me.
>>
>> Usual thing: we cannot differentiate (on the host side) whether the
>> current PSK is _about_ to be replaced; how should the kernel
>> know that the admin will replace the PSK in the next minutes?
>>
>> But that really is an issue with the standard. Currently there is no
>> way how a target could inform the initiator that the credentials have
>> been updated.
> 
> I'd say that the sane thing for the host to do in this case is to reconnect
> until giving up with hope that it may work. This seems like a better 
> approach
> than to abruptly remove the controller no?
> 
>>
>> We would need to define a new status code for this.
>> In the meantime the safe operations model is to set a lifetime
>> for each PSK, and ensure that the PSK is updated on both sides
>> during the lifetime. With that there is a timeframe during which
>> both PSKs are available (on the target), and the older will expire
>> automatically once the lifetime limit is reached.
> 
> That is a good solution, and will also prevent a loss of service until
> the host credentials are updated as well.
> 
> But regardless I have a feeling that simply removing the controller upon
> an authentication error is not the right thing to do here.

Guess what; that's what I tried to do initially. But then Christoph 
objected that we shouldn't generate NVMe status codes internally.
But if we can't do that then we'll have to invent yet another way to 
return a retryable error, leading to even more band-aid.
So I am not quite sure how we could achieve that, short of making 
_every_ error retryable...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich

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