linux-kernel - Re: [PATCH V4 2/5] nvme: add helper interface to flush in-flight requests

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Date:   Thu, 8 Mar 2018 22:44:57 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Ming Lei <tom.leiming@...il.com>
Cc:     Jens Axboe <axboe@...com>, Sagi Grimberg <sagi@...mberg.me>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvme <linux-nvme@...ts.infradead.org>,
        Keith Busch <keith.busch@...el.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH V4 2/5] nvme: add helper interface to flush in-flight
 requests

Hi Ming

Thanks for your precious time for reviewing and comment.

On 03/08/2018 09:11 PM, Ming Lei wrote:
> On Thu, Mar 8, 2018 at 2:19 PM, Jianchao Wang
> <jianchao.w.wang@...cle.com> wrote:
>> Currently, we use nvme_cancel_request to complete the request
>> forcedly. This has following defects:
>>  - It is not safe to race with the normal completion path.
>>    blk_mq_complete_request is ok to race with timeout path,
>>    but not with itself.
> 
> The irq path shouldn't be raced with nvme_cancel_request()
> because io queues are suspended before calling nvme_cancel_request().
> 
> Could you please explain a bit why one same request can be
> completed at the same time via blk_mq_complete_request()?

In fact, this interface will be used before suspend ioqs and disable controller.
Then the timeout path could be more clearly when we issue adminq commands during
nvme_dev_disable. Otherwise, it is hard to distinguish which is from previous workload
, which is from nvme_dev_disable. We will take different action for them.

>>  - Cannot ensure all the requests have been handled. The timeout
>>    path may grab some expired requests, blk_mq_complete_request
>>    cannot touch them.
>>
>> add two helper interface to flush in-flight requests more safely.
>> - nvme_abort_requests_sync
>> use nvme_abort_req to timeout all the in-flight requests and wait
>> until timeout work and irq completion path completes. More details
>> please refer to the comment of this interface.
>> - nvme_flush_aborted_requests
>> complete the requests 'aborted' by nvme_abort_requests_sync. It will
>> be invoked after the controller is disabled/shutdown.
> 
> IMO, the helper's name of 'abort' is very misleading since the request
> isn't aborted actually, it is just cancelled from dispatched state, once
> it is cancelled, most of times the request is just re-inserted to sw
> queue or scheduler queue. After NVMe controller is resetted successfully,
> these request will be dispatched again.
> 
> So please keep the name of 'cancel' or use sort of name.

Yes, it is indeed misleading.
In fact, this 'abort' inherits from the blk_abort_request which is invoked by
nvme_abort_req.
 
Thanks
Jianchao