Re: [PATCH] nvme: reject completions for requests that are not in flight

[Mauricio Faria de Oliveira <mfo@igalia.com>]

On 2026-11-03 16:43, Keith Busch wrote:
> On Tue, Nov 03, 2026 at 04:18:25PM -0300, Mauricio Faria de Oliveira wrote:
>> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
>> index 2d8f681079e85601a92624d196e77f1ba3ace34a..3ba0666da7be6a3de2e5f0fd50155af115b4e1f6 100644
>> --- a/drivers/nvme/host/nvme.h
>> +++ b/drivers/nvme/host/nvme.h
>> @@ -708,6 +708,11 @@ static inline struct request *nvme_find_rq(struct blk_mq_tags *tags,
>>  			tag, genctr, nvme_genctr_mask(nvme_req(rq)->genctr));
>>  		return NULL;
>>  	}
>> +	if (unlikely(blk_mq_rq_state(rq) != MQ_RQ_IN_FLIGHT)) {
>> +		dev_err(nvme_req(rq)->ctrl->device,
>> +			"completion for request %#x not in flight\n", tag);
>> +		return NULL;
>> +	}
>>  	return rq;
>>  }
> 
> Is there something special about the NVMe protocol that makes this
> problem unique to it? If not, why doesn't this check go into the generic
> block layer instead?

Thanks for taking a look.

I noticed you asked the latter question in the previous
submission/review (Link: trailers), and addressed it in the commit
message; pasting it here for reference:

In Chao Shi's patch, there's been feedback/question of whether this
should
be done in blk-mq, as this is not specific to nvme. I'd say no, at
first:
- Some blk-mq calls for completion have no return value (e.g.,
completion
  on other CPUs), which suggests maybe an API change and updates to many
  callers, all for an edge case.
- An alternative available currently might be blk_mq_ops.complete(), but
  that is handled in the driver anyway, with risk of hitting an error in
  blk-mq (like this) as the code changes, and seems semantically wrong,
  i.e., completing a request that should not have been completed.
- Keeping in mind a small fix for stable, for now, should this be
merged.
- But happy to take suggestions if blk-mq is indeed the way to go.

For the former question, I'd imagine other block drivers might be
subject to a similar issue, under incorrect completions, and can take a
look at this later. I'd appreciate feedback on the points above before
trying to address it generically in the block layer, if at all possible.

cheers,

-- 
Mauricio