scsi: core: Register sysfs for SCSI workqueue

Permit scsi_wq_xxx and scsi_tmf_xxx to be bound to different CPUs to get
better isolation.

Use alloc_workqueue with WQ_SYSFS and drop __WQ_ORDERED_EXPLICIT since a
__WQ_ORDERED_EXPLICIT workqueue isn't allowed to change the CPU mask.

Link: https://lore.kernel.org/r/20200701030745.16897-2-bob.liu@oracle.comReviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hosts.c

@@ -272,8 +272,10 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
 	if (shost->transportt->create_work_queue) {
 		snprintf(shost->work_q_name, sizeof(shost->work_q_name),
 			 "scsi_wq_%d", shost->host_no);
-		shost->work_q = create_singlethread_workqueue(
-					shost->work_q_name);
+		shost->work_q = alloc_workqueue("%s",
+			WQ_SYSFS | __WQ_LEGACY | WQ_MEM_RECLAIM | WQ_UNBOUND,
+			1, shost->work_q_name);
+
 		if (!shost->work_q) {
 			error = -EINVAL;
 			goto out_free_shost_data;
@@ -487,7 +489,7 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
 	}
 
 	shost->tmf_work_q = alloc_workqueue("scsi_tmf_%d",
-					    WQ_UNBOUND | WQ_MEM_RECLAIM,
+					WQ_UNBOUND | WQ_MEM_RECLAIM | WQ_SYSFS,
 					   1, shost->host_no);
 	if (!shost->tmf_work_q) {
 		shost_printk(KERN_WARNING, shost,