[PATCH] nvme: don't retry request marked as NVME_REQ_CANCELLED

[jianchao.wang]

Hi ming 

Thanks for your detailed response.
That's really appreciated.

On 01/27/2018 09:31 PM, Ming Lei wrote:
>> But nvme_dev_disable may run with nvme_timeout in parallel or race with it.
> But that doesn't mean it is a race, blk_mq_complete_request() can avoid race
> between timeout and other completions, such as cancel.
> Yes, I know blk_mq_complete_request could avoid the a request is accessed by timeout
path and other completion path concurrently. :)
What's I worry about is the timeout path could hold the expired request, so when
nvme_dev_disable return, we cannot ensure all the previous outstanding requests has been
handled. That's really bad. 

>> The best way to fix this is to ensure the timeout path has been completed before cancel the
>> previously outstanding requests. (Just ignore the case where the nvme_timeout will invoke nvme_dev_disable,
>> it has to be fixed by other way.)
> Maybe your approach looks a bit clean and simplify the implementation, but seems
> it isn't necessary.
> 
> So could you explain a bit what the exact issue you are worrying about? deadlock?
> or others?
There is indeed potential issue. But it is in very narrow window.
Please refer to https://lkml.org/lkml/2018/1/19/68

As you said, the approach looks a bit clean and simplify the implementation.
That's what I really want, break the complicated relationship between 
nvme_timeout and nvme_dev_diable. 

Thanks
Jianchao