[PATCH] nvme-core: fix io interrupt when work with dm-multipah

[Chao Leng]

John, Wat do you think about if delete translate NVME_SC_CMD_INTERRUPTED
to BLK_STS_TARGET? Thank you.

On 2020/7/30 9:49, Chao Leng wrote:
> 
> 
> On 2020/7/29 13:59, Christoph Hellwig wrote:
>> On Wed, Jul 29, 2020 at 10:54:29AM +0800, Chao Leng wrote:
>>>
>>>
>>> On 2020/7/28 19:19, Christoph Hellwig wrote:
>>>> On Mon, Jul 27, 2020 at 01:58:18PM +0800, Chao Leng wrote:
>>>>> The protocol NVM-Express-1.4 define:
>>>>> Command Interrupted: Command processing was interrupted and the
>>>>> controller is unable to successfully complete the command. The host
>>>>> should retry the command. If this status code is returned, then
>>>>> the controller shall clear the Do Not Retry bit to ‘0’ in the Status
>>>>> field of the CQE (refer to Figure 124). The controller shall not return
>>>>> this status code unless the host has set the Advanced Command Retry
>>>>> Enable (ACRE) field to 1h in the Host Behavior Support feature(refer to
>>>>> section 5.21.1.22).
>>>>>
>>>>> According the protocol define, NVME_SC_CMD_INTERRUPTED need retry.
>>>>> The error code NVME_SC_CMD_INTERRUPTED should not translate to
>>>>> BLK_STS_TARGET, because if the error code translate to BLK_STS_TARGET,
>>>>> dm-multipah will return error to application. So if target return error
>>>>> code NVME_SC_CMD_INTERRUPTED, io will interrupt. NVME_SC_CMD_INTERRUPTED
>>>>> should translate to BLK_STS_IOERR by default, dm-multipath will fail
>>>>> over to other path retry the io.
>>>>
>>>> IOERR still seems wrong, though.
>>>> .
>>>
>>> BLK_STS_TARGET means target has critical error. NVME_SC_CMD_INTERRUPTED
>>> just means target need retry io. It is not suitable to translate
>>> NVME_SC_CMD_INTERRUPTED to BLK_STS_TARGET. Maybe translate to
>>> BLK_STS_IOERR is also not suitable, we should translate
>>> NVME_SC_CMD_INTERRUPTED to BLK_STS_AGAIN.
>>> We can do like this:
>>
>> BLK_STS_AGAIN is a bad choice as we use it for calls that block when
>> the callers asked for non-blocking submission.  I'm really not sure
>> we want to change anything here - the error definition clearly states
>> it is not a failure but a request to retry later.
>> .
>>
> BLK_STS_AGAIN is not a good choice, but BLK_STS_TARGET is also not
> a good choice. I find the patch that translate NVME_SC_CMD_INTERRUPTED
> to BLK_STS_TARGET.
> 
> commit:35038bffa87da282010b91108cadd13238bb5bbd
> nvme: Translate more status codes to blk_status_t
> Decode interrupted command and not ready namespace nvme status codes to
> BLK_STS_TARGET. These are not generic IO errors and should use a non-path
> specific error so that it can use the non-failover retry path.
> Reported-by: John Meneghini <John.Meneghini at netapp.com>
> 
> In the old version, need translate NVME_SC_CMD_INTERRUPTED to
> BLK_STS_TARGET, because nvme multipath check the blk_path_error,
> we expect retry IO in the current path, so have to translate
> NVME_SC_CMD_INTERRUPTED to BLK_STS_TARGET. Although converting to
> BLK_STS_TARGET is not a good choice, there seems to be no better choice
> for the old version code. But now we do not need translate
> NVME_SC_CMD_INTERRUPTED to BLK_STS_TARGET, nvme multipath already
> improve and does not depend on blk_path_error.
> 
> According to the description of BLK_STS_TARGET:
> [BLK_STS_TARGET]    = { -EREMOTEIO,    "critical target" }
> BLK_STS_TARGET may easily mistaken as a fatal error on the storage.
> I already check all the error code of BLK_STS_xx, there is no good
> choice for NVME_SC_CMD_INTERRUPTED now. In the absence of a suitable
> error code, it is a good choice to retain the default. So I strongly
> suggest delete translate NVME_SC_CMD_INTERRUPTED to BLK_STS_TARGET.
> 
> John, what do you think?