Re: [PATCHv2 1/3] block: introduce rq_list_for_each_safe macro

[Keith Busch <kbusch@kernel.org>]

On Mon, Jan 03, 2022 at 05:23:08PM +0200, Max Gurtovoy wrote:
> On 12/30/2021 5:30 PM, Keith Busch wrote:
> > I think it just may work if we export blk_mq_get_driver_tag().
> 
> do you have a suggestion for the NVMe/PCI driver ?

The following tests fine with my multi-namespace setups. I have real
hardware with namespace management capabilities, but qemu can also
easily emulate it too for anyone who doesn't have one.

---
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index 5668e28be0b7..84f2e73d0c7c 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -41,12 +41,6 @@ static inline struct sbq_wait_state *bt_wait_ptr(struct sbitmap_queue *bt,
 	return sbq_wait_ptr(bt, &hctx->wait_index);
 }
 
-enum {
-	BLK_MQ_NO_TAG		= -1U,
-	BLK_MQ_TAG_MIN		= 1,
-	BLK_MQ_TAG_MAX		= BLK_MQ_NO_TAG - 1,
-};
-
 extern bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *);
 extern void __blk_mq_tag_idle(struct blk_mq_hw_ctx *);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0d7c9d3e0329..b4540723077a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1589,6 +1589,7 @@ bool __blk_mq_get_driver_tag(struct blk_mq_hw_ctx *hctx, struct request *rq)
 	hctx->tags->rqs[rq->tag] = rq;
 	return true;
 }
+EXPORT_SYMBOL_GPL(__blk_mq_get_driver_tag);
 
 static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,
 				int flags, void *key)
@@ -2582,11 +2583,10 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 		 * same queue, caller must ensure that's the case.
 		 *
 		 * Since we pass off the full list to the driver at this point,
-		 * we do not increment the active request count for the queue.
-		 * Bypass shared tags for now because of that.
+		 * we are counting on the driver to increment the active
+		 * request count for the queue.
 		 */
-		if (q->mq_ops->queue_rqs &&
-		    !(rq->mq_hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)) {
+		if (q->mq_ops->queue_rqs) {
 			blk_mq_run_dispatch_ops(q,
 				__blk_mq_flush_plug_list(q, plug));
 			if (rq_list_empty(plug->mq_list))
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 948791ea2a3e..0f37ae906901 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -268,21 +268,6 @@ static inline void blk_mq_put_driver_tag(struct request *rq)
 	__blk_mq_put_driver_tag(rq->mq_hctx, rq);
 }
 
-bool __blk_mq_get_driver_tag(struct blk_mq_hw_ctx *hctx, struct request *rq);
-
-static inline bool blk_mq_get_driver_tag(struct request *rq)
-{
-	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
-
-	if (rq->tag != BLK_MQ_NO_TAG &&
-	    !(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)) {
-		hctx->tags->rqs[rq->tag] = rq;
-		return true;
-	}
-
-	return __blk_mq_get_driver_tag(hctx, rq);
-}
-
 static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
 {
 	int cpu;
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 50deb8b69c40..f50483475c12 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -992,8 +992,9 @@ static bool nvme_prep_rq_batch(struct nvme_queue *nvmeq, struct request *req)
 		return false;
 	if (unlikely(!nvme_check_ready(&nvmeq->dev->ctrl, req, true)))
 		return false;
+	if (!blk_mq_get_driver_tag(req))
+		return false;
 
-	req->mq_hctx->tags->rqs[req->tag] = req;
 	return nvme_prep_rq(nvmeq->dev, req) == BLK_STS_OK;
 }
 
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 550996cf419c..8fb544a35330 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -1072,6 +1072,27 @@ static inline int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 }
 void blk_dump_rq_flags(struct request *, char *);
 
+enum {
+	BLK_MQ_NO_TAG		= -1U,
+	BLK_MQ_TAG_MIN		= 1,
+	BLK_MQ_TAG_MAX		= BLK_MQ_NO_TAG - 1,
+};
+
+bool __blk_mq_get_driver_tag(struct blk_mq_hw_ctx *hctx, struct request *rq);
+
+static inline bool blk_mq_get_driver_tag(struct request *rq)
+{
+	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
+
+	if (rq->tag != BLK_MQ_NO_TAG &&
+	    !(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)) {
+		hctx->tags->rqs[rq->tag] = rq;
+		return true;
+	}
+
+	return __blk_mq_get_driver_tag(hctx, rq);
+}
+
 #ifdef CONFIG_BLK_DEV_ZONED
 static inline unsigned int blk_rq_zone_no(struct request *rq)
 {
--