Messages in this thread | | | Subject | Re: [PATCH 5/7] blk-mq: remove REQ_ATOM_COMPLETE usages from blk-mq | From | "jianchao.wang" <> | Date | Tue, 9 Jan 2018 11:08:04 +0800 |
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Hi tejun
Many thanks for you kindly response.
On 01/09/2018 01:27 AM, Tejun Heo wrote: > Hello, Jianchao. > > On Fri, Dec 22, 2017 at 12:02:20PM +0800, jianchao.wang wrote: >>> On Thu, Dec 21, 2017 at 11:56:49AM +0800, jianchao.wang wrote: >>>> It's worrying that even though the blk_mark_rq_complete() here is >>>> intended to synchronize with timeout path, but it indeed give the >>>> blk_mq_complete_request() the capability to exclude with >> >> There could be scenario where the driver itself stop a request >> itself with blk_mq_complete_request() or some other interface that >> will invoke it, races with the normal completion path where a same >> request comes. > > But what'd prevent the completion reinitializing the request and then > the actual completion path coming in and completing the request again? > blk_mark_rq_complete() will gate and ensure there will be only one __blk_mq_complete_request() to be invoked.
>> For example: >> a reset could be triggered through sysfs on nvme-rdma >> Then the driver will cancel all the reqs, including in-flight ones. >> nvme_rdma_reset_ctrl_work() >> nvme_rdma_shutdown_ctrl() >> >>>> >> if (ctrl->ctrl.queue_count > 1) { >> nvme_stop_queues(&ctrl->ctrl); //quiesce the queue >> blk_mq_tagset_busy_iter(&ctrl->tag_set, >> nvme_cancel_request, &ctrl->ctrl); //invoke blk_mq_complete_request() >> nvme_rdma_destroy_io_queues(ctrl, shutdown); >> } >> >>>> >> >> These operations could race with the normal completion path of in-flight ones. >> It should drain all the in-flight ones first here. But there maybe some other >> places similar with this. > > If there are any such places, they should be using an interface which > is propelry synchronized like blk_abort_request(), which btw is what > libata already does. Otherwise, it's racy with or without these > patches. Yes, it is that.
Thanks for you kindly response again. Jianchao
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