Re: [PATCH] blk-mq: Return invalid cookie if bio was split

[Keith Busch <keith.busch@intel.com>]

On Wed, Oct 05, 2016 at 11:19:39AM +0800, Ming Lei wrote:
> But .poll() need to check if the specific request is completed or not,
> then blk_poll() can set 'current' as RUNNING if it is completed.
> 
> blk_poll():
>                 ...
>                 ret = q->mq_ops->poll(hctx, blk_qc_t_to_tag(cookie));
>                 if (ret > 0) {
>                         hctx->poll_success++;
>                         set_current_state(TASK_RUNNING);
>                         return true;
>                 }


Right, but the task could be waiting on a whole lot more than just that
one tag, so setting the task to running before knowing those all complete
doesn't sound right.
 
> I am glad to take a look the patch if you post it out.

Here's what I got for block + nvme. It relies on all the requests to
complete to set the task back to running.

---
diff --git a/block/blk-core.c b/block/blk-core.c
index b993f88..3c1cfbf 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -3342,6 +3342,8 @@ EXPORT_SYMBOL(blk_finish_plug);
 bool blk_poll(struct request_queue *q, blk_qc_t cookie)
 {
 	struct blk_plug *plug;
+	struct blk_mq_hw_ctx *hctx;
+	unsigned int queue_num;
 	long state;
 
 	if (!q->mq_ops || !q->mq_ops->poll || !blk_qc_t_valid(cookie) ||
@@ -3353,27 +3355,15 @@ bool blk_poll(struct request_queue *q, blk_qc_t cookie)
 		blk_flush_plug_list(plug, false);
 
 	state = current->state;
+	queue_num = blk_qc_t_to_queue_num(cookie);
+	hctx = q->queue_hw_ctx[queue_num];
 	while (!need_resched()) {
-		unsigned int queue_num = blk_qc_t_to_queue_num(cookie);
-		struct blk_mq_hw_ctx *hctx = q->queue_hw_ctx[queue_num];
-		int ret;
-
-		hctx->poll_invoked++;
-
-		ret = q->mq_ops->poll(hctx, blk_qc_t_to_tag(cookie));
-		if (ret > 0) {
-			hctx->poll_success++;
-			set_current_state(TASK_RUNNING);
-			return true;
-		}
+		q->mq_ops->poll(hctx);
 
 		if (signal_pending_state(state, current))
 			set_current_state(TASK_RUNNING);
-
 		if (current->state == TASK_RUNNING)
 			return true;
-		if (ret < 0)
-			break;
 		cpu_relax();
 	}
 
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index befac5b..2e359e0 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -649,7 +651,7 @@ static inline bool nvme_cqe_valid(struct nvme_queue *nvmeq, u16 head,
 	return (le16_to_cpu(nvmeq->cqes[head].status) & 1) == phase;
 }
 
-static void __nvme_process_cq(struct nvme_queue *nvmeq, unsigned int *tag)
+static void nvme_process_cq(struct nvme_queue *nvmeq)
 {
 	u16 head, phase;
 
@@ -665,9 +667,6 @@ static void __nvme_process_cq(struct nvme_queue *nvmeq, unsigned int *tag)
 			phase = !phase;
 		}
 
-		if (tag && *tag == cqe.command_id)
-			*tag = -1;
-
 		if (unlikely(cqe.command_id >= nvmeq->q_depth)) {
 			dev_warn(nvmeq->dev->ctrl.device,
 				"invalid id %d completed on queue %d\n",
@@ -711,11 +710,6 @@ static void __nvme_process_cq(struct nvme_queue *nvmeq, unsigned int *tag)
 	nvmeq->cqe_seen = 1;
 }
 
-static void nvme_process_cq(struct nvme_queue *nvmeq)
-{
-	__nvme_process_cq(nvmeq, NULL);
-}
-
 static irqreturn_t nvme_irq(int irq, void *data)
 {
 	irqreturn_t result;
@@ -736,20 +730,15 @@ static irqreturn_t nvme_irq_check(int irq, void *data)
 	return IRQ_NONE;
 }
 
-static int nvme_poll(struct blk_mq_hw_ctx *hctx, unsigned int tag)
+static void nvme_poll(struct blk_mq_hw_ctx *hctx)
 {
 	struct nvme_queue *nvmeq = hctx->driver_data;
 
 	if (nvme_cqe_valid(nvmeq, nvmeq->cq_head, nvmeq->cq_phase)) {
 		spin_lock_irq(&nvmeq->q_lock);
-		__nvme_process_cq(nvmeq, &tag);
+		nvme_process_cq(nvmeq);
 		spin_unlock_irq(&nvmeq->q_lock);
-
-		if (tag == -1)
-			return 1;
 	}
-
-	return 0;
 }
 
 static void nvme_pci_submit_async_event(struct nvme_ctrl *ctrl, int aer_idx)
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 2498fdf..a723af9 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -100,7 +100,7 @@ typedef void (exit_request_fn)(void *, struct request *, unsigned int,
 typedef void (busy_iter_fn)(struct blk_mq_hw_ctx *, struct request *, void *,
 		bool);
 typedef void (busy_tag_iter_fn)(struct request *, void *, bool);
-typedef int (poll_fn)(struct blk_mq_hw_ctx *, unsigned int);
+typedef void (poll_fn)(struct blk_mq_hw_ctx *);
 
 
 struct blk_mq_ops {
--