From e5edd5f298fafda28284bafb8371e6f0b7681035 Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@redhat.com>
Date: Tue, 18 Dec 2018 01:28:56 +0800
Subject: [PATCH] blk-mq: skip zero-queue maps in blk_mq_map_swqueue

From 7e849dd9cf37 ("nvme-pci: don't share queue maps"), the mapping
table won't be initialized actually if map->nr_queues is zero, so
we can't use blk_mq_map_queue_type() to retrieve hctx any more.

This way still may cause broken mapping, fix it by skipping zero-queues
maps in blk_mq_map_swqueue().

Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 block/blk-mq.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9c1c1544bac3..6847f014606b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2438,6 +2438,9 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 
 		ctx = per_cpu_ptr(q->queue_ctx, i);
 		for (j = 0; j < set->nr_maps; j++) {
+			if (!set->map[j].nr_queues)
+				continue;
+
 			hctx = blk_mq_map_queue_type(q, j, i);
 
 			/*