Message-ID: <9b01b4b3-0beb-4159-1ce9-4ed4b531d7a6@suse.de>
Date:   Tue, 27 Jun 2023 08:51:49 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Daniel Wagner <dwagner@...e.de>,
        Dan Carpenter <dan.carpenter@...aro.org>
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, Chaitanya Kulkarni <kch@...dia.com>,
        Shin'ichiro Kawasaki <shinichiro@...tmail.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        James Smart <jsmart2021@...il.com>
Subject: Re: [PATCH v2 4/5] nvme-fc: Make initial connect attempt synchronous

On 6/27/23 08:39, Hannes Reinecke wrote:
> On 6/27/23 08:18, Daniel Wagner wrote:
>> On Mon, Jun 26, 2023 at 02:33:18PM +0300, Dan Carpenter wrote:
>>>> @@ -2943,6 +2943,8 @@ nvme_fc_create_io_queues(struct nvme_fc_ctrl 
>>>> *ctrl)
>>>>       /* force put free routine to ignore io queues */
>>>>       ctrl->ctrl.tagset = NULL;
>>>> +    if (ret > 0)
>>>> +        ret = -EIO;
>>>
>>> All these checks for ret > 0 make me unhappy.  I don't understand how
>>> they are a part of the commit.
>>
>> We have two types of error message types in the nvme subsystem. The 
>> negative
>> values are the usual ones and positive ones are nvme protocol errors.
>>
>> For example if the authentication fails because of invalid credentials 
>> when
>> doing the authentication nvmf_connect_admin_queue() will return a 
>> value of
>> NVME_SC_AUTH_REQUIRED. This is also the value which gets propagated to 
>> this
>> point here. The problem is any positive error code is interpreted as a 
>> valid
>> pointer later in the code, which results in a crash.
>>
>>> I have tried to look at the context and I think maybe you are working
>>> around the fact that qla_nvme_ls_req() returns QLA_FUNCTION_FAILED on
>>> error.
>>
>> The auth blktests are exercising the error path here and that's why I 
>> added
>> this check. BTW, we already use in other places, this is not 
>> completely new in
>> this subsystem.
>>
>>> Also the qla_nvme_ls_req() function EINVAL on error.  I just wrote a
>>> commit message saying that none of the callers cared but I missed that
>>> apparently gets returned to nvme_fc_init_ctrl().  :/
>>> https://lore.kernel.org/all/49866d28-4cfe-47b0-842b-78f110e61aab@moroto.mountain/
>>
>> Thank!
>>
>>> Let's just fix qla_nvme_ls_req() instead of working around it here.
>>>
>>> And let's add a WARN_ON_ONCE() somewhere to prevent future bugs.
>>
>> This makes sense for the driver APIs. Though for the core nvme 
>> subsystem this
>> needs to be discusses/redesigned how to handle the protocol errors first.
>>
> I would stick with the 'normal' nvme syntax of having negative errors as 
> internal errors (ie errnos), '0' for no error, and positive numbers as 
> NVMe protocol errors.
> As such I would also advocate to not map NVMe protocol errors onto error 
> numbers but rather fix the callers to not do a pointer conversion.
> 
Aw. Now I see it.

It's the ->create_ctrl() callback which will always return a controller 
pointer or an error value.
If we were to return a protocol error we would need to stick it into the 
controller structure itself. But if we doing that then we'll be ending 
up with a non-existing controller, ie we'd be returning a structure for 
a dead controller. Not exactly pretty, but it would allow us to improve
the userland API to return the NVMe protocol error by reading from the
fabrics device; the controller structure itself would be cleaned up when 
closing that device.

Hmm.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@...e.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman

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