scsi: megaraid: Clear READ queue map's nr_queues

The megaraid SCSI driver sets set->nr_maps as 3 if poll_queues is > 0, and
blk-mq actually initializes each map's nr_queues as nr_hw_queues.
Consequently the driver has to clear READ queue map's nr_queues, otherwise
the queue map becomes broken if poll_queues is set as non-zero.

Link: https://lore.kernel.org/r/[email protected]
Fixes: 9e4bec5 ("scsi: megaraid_sas: mq_poll support")
Cc: Kashyap Desai <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Hannes Reinecke <[email protected]>
Reported-by: Guangwu Zhang <[email protected]>
Tested-by: Guangwu Zhang <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: Ming Lei

drivers/scsi/megaraid/megaraid_sas_base.c

@@ -3195,6 +3195,9 @@ static int megasas_map_queues(struct Scsi_Host *shost)
 	qoff += map->nr_queues;
 	offset += map->nr_queues;
 
+	/* we never use READ queue, so can't cheat blk-mq */
+	shost->tag_set.map[HCTX_TYPE_READ].nr_queues = 0;
+
 	/* Setup Poll hctx */
 	map = &shost->tag_set.map[HCTX_TYPE_POLL];
 	map->nr_queues = instance->iopoll_q_count;