[dm-devel] nvme: explicitly use normal NVMe error handling when appropriate

[Chao Leng]

On 2020/8/11 12:20, Mike Snitzer wrote:
> On Mon, Aug 10 2020 at 11:32pm -0400,
> Chao Leng <lengchao at huawei.com> wrote:
> 
>>
>>
>> On 2020/8/11 1:22, Mike Snitzer wrote:
>>> On Mon, Aug 10 2020 at 10:36am -0400,
>>> Mike Snitzer <snitzer at redhat.com> wrote:
>>>
>>>> On Fri, Aug 07 2020 at  7:35pm -0400,
>>>> Sagi Grimberg <sagi at grimberg.me> wrote:
>>>>
>>>>>
>>>>>>> Hey Mike,
>>> ...
>>>>>> I think NVMe can easily fix this by having an earlier stage of checking,
>>>>>> e.g. nvme_local_retry_req(), that shortcircuits ever getting to
>>>>>> higher-level multipathing consideration (be it native NVMe or DM
>>>>>> multipathing) for cases like NVME_SC_CMD_INTERRUPTED.
>>>>>> To be clear: the "default" case of nvme_failover_req() that returns
>>>>>> false to fallback to NVMe's "local" normal NVMe error handling -- that
>>>>>> can stay.. but a more explicit handling of cases like
>>>>>> NVME_SC_CMD_INTERRUPTED should be added to a nvme_local_retry_req()
>>>>>> check that happens before nvme_failover_req() in nvme_complete_rq().
>>>>>
>>>>> I don't necessarily agree with having a dedicated nvme_local_retry_req().
>>>>> a request that isn't failed over, goes to local error handling (retry or
>>>>> not). I actually think that just adding the condition to
>>>>> nvme_complete_req and having nvme_failover_req reject it would work.
>>>>>
>>>>> Keith?
>>>>
>>>> I think that is basically what I'm thinking too.
>>>
>>> From: Mike Snitzer <snitzer at redhat.com>
>>> Subject: nvme: explicitly use normal NVMe error handling when appropriate
>>>
>>> Commit 764e9332098c0 ("nvme-multipath: do not reset on unknown
>>> status"), among other things, fixed NVME_SC_CMD_INTERRUPTED error
>>> handling by changing multipathing's nvme_failover_req() to short-circuit
>>> path failover and then fallback to NVMe's normal error handling (which
>>> takes care of NVME_SC_CMD_INTERRUPTED).
>>>
>>> This detour through native NVMe multipathing code is unwelcome because
>>> it prevents NVMe core from handling NVME_SC_CMD_INTERRUPTED independent
>>> of any multipathing concerns.
>>>
>>> Introduce nvme_status_needs_local_error_handling() to prioritize
>>> non-failover retry, when appropriate, in terms of normal NVMe error
>>> handling.  nvme_status_needs_local_error_handling() will naturely evolve
>>> to include handling of any other errors that normal error handling must
>>> be used for.
>>>
>>> nvme_failover_req()'s ability to fallback to normal NVMe error handling
>>> has been preserved because it may be useful for future NVME_SC that
>>> nvme_status_needs_local_error_handling() hasn't yet been trained for.
>>>
>>> Signed-off-by: Mike Snitzer <snitzer at redhat.com>
>>> ---
>>>   drivers/nvme/host/core.c | 16 ++++++++++++++--
>>>   1 file changed, 14 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>>> index 88cff309d8e4..be749b690af7 100644
>>> --- a/drivers/nvme/host/core.c
>>> +++ b/drivers/nvme/host/core.c
>>> @@ -252,6 +252,16 @@ static inline bool nvme_req_needs_retry(struct request *req)
>>>   	return true;
>>>   }
>>> +static inline bool nvme_status_needs_local_error_handling(u16 status)
>>> +{
>>> +	switch (status & 0x7ff) {
>>> +	case NVME_SC_CMD_INTERRUPTED:
>>> +		return true;
>>> +	default:
>>> +		return false;
>>> +	}
>>> +}
>>> +
>>>   static void nvme_retry_req(struct request *req)
>>>   {
>>>   	struct nvme_ns *ns = req->q->queuedata;
>>> @@ -270,7 +280,8 @@ static void nvme_retry_req(struct request *req)
>>>   void nvme_complete_rq(struct request *req)
>>>   {
>>> -	blk_status_t status = nvme_error_status(nvme_req(req)->status);
>>> +	u16 nvme_status = nvme_req(req)->status;
>>> +	blk_status_t status = nvme_error_status(nvme_status);
>>>   	trace_nvme_complete_rq(req);
>>> @@ -280,7 +291,8 @@ void nvme_complete_rq(struct request *req)
>>>   		nvme_req(req)->ctrl->comp_seen = true;
>>>   	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
>>> -		if ((req->cmd_flags & REQ_NVME_MPATH) && nvme_failover_req(req))
>>> +		if (!nvme_status_needs_local_error_handling(nvme_status) &&
>>> +		    (req->cmd_flags & REQ_NVME_MPATH) && nvme_failover_req(req))
>>
>> This looks no affect. if work with nvme multipath, now is already retry local.
> 
> Not if NVMe is built without multipathing configured.
If without nvme multipathing configured, now is also retry local, do not need
!nvme_status_needs_local_error_handling(nvme_status).
> 
>> If work with dm-multipath, still return error.
> 
> Yes, I'm aware.  Use of REQ_FAILFAST_TRANSPORT isn't something that is
> needed for NVMe, so why are you proposing hacks in NVMe to deal with it?
I just describe the possible scenarios:1.nvme multipathing configured.
2.without any multipath.3. with dm-multipath.
> 
>>>   			return;
>>>   		if (!blk_queue_dying(req->q)) {
>>>
>>
>> Suggest:
>> REQ_FAILFAST_TRANSPORT may be designed for scsi, because scsi protocol
>> do not difine the local retry mechanism. SCSI implements a fuzzy local
>> retry mechanism, so need the REQ_FAILFAST_TRANSPORT for multipath
>> software, multipath software retry according error code is expected.
>> nvme is different with scsi about this. It define local retry mechanism
>> and path error code, so nvme should not care REQ_FAILFAST_TRANSPORT.
> 
> Exactly.  Except by "nvme should not care REQ_FAILFAST_TRANSPORT." your
> patch says you mean "nvme shouldn't disallow retry if
> REQ_FAILFAST_TRANSPORT is it".  I'm saying: don't try to get such
> changes into NVMe.
no. the patch just mean: if path error, fail over to retry by multipath
(nvme multipath or dm-multipath). Other need local retry local, retry
after a defined time according to status(CRD) and CRDT. Now nvme multipath
is already do like this, the patch make dm-multipath work like nvme multipath.
> 
> In general, aspects of your patch may have merit but overall it is doing
> too much.
> 
> Mike
> 
> .
>