Revert "scsi: default to scsi-mq"

Defaulting to scsi-mq in 4.13-rc has shown various regressions
on setups that we didn't previously consider.  Fixes for them are
in progress, but too invasive to make it in this cycle.  So for
now revert the commit that defaults to blk-mq for SCSI.  For 4.14
we'll plan to try again with these fixes.

This reverts commit 5c279bd9e4.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/Kconfig

@@ -47,6 +47,17 @@ config SCSI_NETLINK
 	default	n
 	depends on NET
 
+config SCSI_MQ_DEFAULT
+	bool "SCSI: use blk-mq I/O path by default"
+	depends on SCSI
+	---help---
+	  This option enables the new blk-mq based I/O path for SCSI
+	  devices by default.  With the option the scsi_mod.use_blk_mq
+	  module/boot option defaults to Y, without it to N, but it can
+	  still be overridden either way.
+
+	  If unsure say N.
+
 config SCSI_PROC_FS
 	bool "legacy /proc/scsi/ support"
 	depends on SCSI && PROC_FS

drivers/scsi/scsi.c

@@ -800,7 +800,11 @@ MODULE_LICENSE("GPL");
 module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");
 
+#ifdef CONFIG_SCSI_MQ_DEFAULT
 bool scsi_use_blk_mq = true;
+#else
+bool scsi_use_blk_mq = false;
+#endif
 module_param_named(use_blk_mq, scsi_use_blk_mq, bool, S_IWUSR | S_IRUGO);
 
 static int __init init_scsi(void)