linux-kernel - Re: [RFC PATCH 3/3] nvme: Introduce nvme_execute_passthru_rq

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Date:   Fri, 25 Oct 2019 14:40:20 -0700
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org
Cc:     Keith Busch <kbusch@...nel.org>, Max Gurtovoy <maxg@...lanox.com>,
        Christoph Hellwig <hch@....de>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [RFC PATCH 3/3] nvme: Introduce nvme_execute_passthru_rq_nowait()


>>> +#ifdef CONFIG_NVME_TARGET_PASSTHRU
>>> +static void nvme_execute_passthru_rq_work(struct work_struct *w)
>>> +{
>>> +    struct nvme_request *req = container_of(w, struct nvme_request,
>>> work);
>>> +    struct request *rq = blk_mq_rq_from_pdu(req);
>>> +    rq_end_io_fn *done = rq->end_io;
>>> +    void *end_io_data = rq->end_io_data;
>>
>> Why is end_io_data stored to a local variable here? where is it set?
> 
> blk_execute_rq() (which is called by nvme_execute_rq()) will overwrite
> rq->endio and rq->end_io_data. We store them here so we can call the
> callback appropriately after the request completes. It would be set by
> the caller in the same way they set it if they were calling
> blk_execute_rq_nowait().

I see..

>>> +
>>> +    nvme_execute_passthru_rq(rq);
>>> +
>>> +    if (done) {
>>> +        rq->end_io_data = end_io_data;
>>> +        done(rq, 0);
>>> +    }
>>> +}
>>> +
>>> +void nvme_execute_passthru_rq_nowait(struct request *rq, rq_end_io_fn
>>> *done)
>>> +{
>>> +    struct nvme_command *cmd = nvme_req(rq)->cmd;
>>> +    struct nvme_ctrl *ctrl = nvme_req(rq)->ctrl;
>>> +    struct nvme_ns *ns = rq->q->queuedata;
>>> +    struct gendisk *disk = ns ? ns->disk : NULL;
>>> +    u32 effects;
>>> +
>>> +    /*
>>> +     * This function may be called in interrupt context, so we cannot
>>> sleep
>>> +     * but nvme_passthru_[start|end]() may sleep so we need to execute
>>> +     * the command in a work queue.
>>> +     */
>>> +    effects = nvme_command_effects(ctrl, ns, cmd->common.opcode);
>>> +    if (effects) {
>>> +        rq->end_io = done;
>>> +        INIT_WORK(&nvme_req(rq)->work, nvme_execute_passthru_rq_work);
>>> +        queue_work(nvme_wq, &nvme_req(rq)->work);
>>
>> This work will need to be flushed when in nvme_stop_ctrl. That is
>> assuming that it will fail-fast and not hang (which it should given
>> that its a passthru command that is allocated via nvme_alloc_request).
> 
> Hmm, that's going to be a bit tricky. Seeing the work_struct belongs
> potentially to a number of different requests, we can't just flush the
> individual work items. I think we'd have to create a work-queue per ctrl
> and flush that. Any objections to that?

I'd object to that overhead...

How about marking the request if the workqueue path is taken and
in nvme_stop_ctrl you add a blk_mq_tagset_busy_iter and cancel
it in the callback?

Something like:
--
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index fa7ba09dca77..13dbbec5497d 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3955,12 +3955,33 @@ void nvme_complete_async_event(struct nvme_ctrl 
*ctrl, __le16 status,
  }
  EXPORT_SYMBOL_GPL(nvme_complete_async_event);

+static bool nvme_flush_async_passthru_request(struct request *rq,
+               void *data, bool reserved)
+{
+       if (!(nvme_req(rq)->flags & NVME_REQ_ASYNC_PASSTHRU))
+               return true;
+
+       dev_dbg_ratelimited(((struct nvme_ctrl *) data)->device,
+                               "Cancelling passthru I/O %d", req->tag);
+       flush_work(&nvme_req(rq)->work);
+       return true;
+}
+
+static void nvme_flush_async_passthru_requests(struct nvme_ctrl *ctrl)
+{
+       blk_mq_tagset_busy_iter(ctrl->tagset,
+               nvme_flush_async_passthru_request, ctrl);
+       blk_mq_tagset_busy_iter(ctrl->admin_tagset,
+               nvme_flush_async_passthru_request, ctrl);
+}
+
  void nvme_stop_ctrl(struct nvme_ctrl *ctrl)
  {
         nvme_mpath_stop(ctrl);
         nvme_stop_keep_alive(ctrl);
         flush_work(&ctrl->async_event_work);
         cancel_work_sync(&ctrl->fw_act_work);
+       nvme_flush_async_passthru_requests(ctrl);
  }
  EXPORT_SYMBOL_GPL(nvme_stop_ctrl);
--