Re: [PATCH 3/4] blk-mq: deal with shared queue mapping reliably

[Christoph Hellwig <hch@lst.de>]

I suspect we want something like this to make sure we never look
at queue maps that don't have nr_queues set, and then just don't
have to initialize them in nvme:

diff --git a/block/blk-mq.h b/block/blk-mq.h
index b63a0de8a07a..d1ed096723fb 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -105,14 +105,17 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
 {
 	enum hctx_type type = HCTX_TYPE_DEFAULT;
 
-	if (q->tag_set->nr_maps > HCTX_TYPE_POLL &&
-	    ((flags & REQ_HIPRI) && test_bit(QUEUE_FLAG_POLL, &q->queue_flags)))
+	if ((flags & REQ_HIPRI) &&
+	    q->tag_set->nr_maps > HCTX_TYPE_POLL && 
+	    q->tag_set->map[HCTX_TYPE_POLL].nr_queues &&
+	    test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
 		type = HCTX_TYPE_POLL;
 
-	else if (q->tag_set->nr_maps > HCTX_TYPE_READ &&
-		 ((flags & REQ_OP_MASK) == REQ_OP_READ))
+	else if (((flags & REQ_OP_MASK) == REQ_OP_READ) &&
+	         q->tag_set->nr_maps > HCTX_TYPE_READ &&
+		 q->tag_set->map[HCTX_TYPE_READ].nr_queues)
 		type = HCTX_TYPE_READ;
-
+	
 	return blk_mq_map_queue_type(q, type, cpu);
 }
 
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index fb9d8270f32c..698b350b38cf 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -496,11 +496,7 @@ static int nvme_pci_map_queues(struct blk_mq_tag_set *set)
 		map->nr_queues = dev->io_queues[i];
 		if (!map->nr_queues) {
 			BUG_ON(i == HCTX_TYPE_DEFAULT);
-
-			/* shared set, resuse read set parameters */
-			map->nr_queues = dev->io_queues[HCTX_TYPE_DEFAULT];
-			qoff = 0;
-			offset = queue_irq_offset(dev);
+			continue;
 		}
 
 		/*