target: Convert se_device statistics to atomic_long_t

This patch converts the handful of se_device statistics to type
atomic_long_t, instead of using se_device->stats_lock when
incrementing these values.

More importantly, go ahead and drop the spinlock usage within
transport_lookup_cmd_lun() fast-path code.

Signed-off-by: Nicholas Bellinger <[e-mail]>

drivers/target/target_core_device.c

···
 	/* Directly associate cmd with se_dev */
 	se_cmd->se_dev = se_lun->lun_se_dev;
 
-	/* TODO: get rid of this and use atomics for stats */
 	dev = se_lun->lun_se_dev;
-	spin_lock_irqsave(&dev->stats_lock, flags);
-	dev->num_cmds++;
+	atomic_long_inc(&dev->num_cmds);
 	if (se_cmd->data_direction == DMA_TO_DEVICE)
-		dev->write_bytes += se_cmd->data_length;
+		atomic_long_add(se_cmd->data_length, &dev->write_bytes);
 	else if (se_cmd->data_direction == DMA_FROM_DEVICE)
-		dev->read_bytes += se_cmd->data_length;
-	spin_unlock_irqrestore(&dev->stats_lock, flags);
+		atomic_long_add(se_cmd->data_length, &dev->read_bytes);
 
 	return 0;
 }
···
 	INIT_LIST_HEAD(&dev->state_list);
 	INIT_LIST_HEAD(&dev->qf_cmd_list);
 	INIT_LIST_HEAD(&dev->g_dev_node);
-	spin_lock_init(&dev->stats_lock);
 	spin_lock_init(&dev->execute_task_lock);
 	spin_lock_init(&dev->delayed_cmd_lock);
 	spin_lock_init(&dev->dev_reservation_lock);

drivers/target/target_core_stat.c

···
 	struct se_device *dev =
 		container_of(sgrps, struct se_device, dev_stat_grps);
 
-	return snprintf(page, PAGE_SIZE, "%u\n", dev->num_resets);
+	return snprintf(page, PAGE_SIZE, "%lu\n",
+			atomic_long_read(&dev->num_resets));
 }
 DEV_STAT_SCSI_TGT_DEV_ATTR_RO(resets);
 
···
 		container_of(sgrps, struct se_device, dev_stat_grps);
 
 	/* scsiLuNumCommands */
-	return snprintf(page, PAGE_SIZE, "%llu\n",
-			(unsigned long long)dev->num_cmds);
+	return snprintf(page, PAGE_SIZE, "%lu\n",
+			atomic_long_read(&dev->num_cmds));
 }
 DEV_STAT_SCSI_LU_ATTR_RO(num_cmds);
 
···
 		container_of(sgrps, struct se_device, dev_stat_grps);
 
 	/* scsiLuReadMegaBytes */
-	return snprintf(page, PAGE_SIZE, "%u\n", (u32)(dev->read_bytes >> 20));
+	return snprintf(page, PAGE_SIZE, "%lu\n",
+			atomic_long_read(&dev->read_bytes) >> 20);
 }
 DEV_STAT_SCSI_LU_ATTR_RO(read_mbytes);
 
···
 		container_of(sgrps, struct se_device, dev_stat_grps);
 
 	/* scsiLuWrittenMegaBytes */
-	return snprintf(page, PAGE_SIZE, "%u\n", (u32)(dev->write_bytes >> 20));
+	return snprintf(page, PAGE_SIZE, "%lu\n",
+			atomic_long_read(&dev->write_bytes) >> 20);
 }
 DEV_STAT_SCSI_LU_ATTR_RO(write_mbytes);
 
···
 		container_of(sgrps, struct se_device, dev_stat_grps);
 
 	/* scsiLuInResets */
-	return snprintf(page, PAGE_SIZE, "%u\n", dev->num_resets);
+	return snprintf(page, PAGE_SIZE, "%lu\n", atomic_long_read(&dev->num_resets));
 }
 DEV_STAT_SCSI_LU_ATTR_RO(resets);
 

drivers/target/target_core_tmr.c

···
 		pr_debug("LUN_RESET: SCSI-2 Released reservation\n");
 	}
 
-	spin_lock_irq(&dev->stats_lock);
-	dev->num_resets++;
-	spin_unlock_irq(&dev->stats_lock);
+	atomic_long_inc(&dev->num_resets);
 
 	pr_debug("LUN_RESET: %s for [%s] Complete\n",
 			(preempt_and_abort_list) ? "Preempt" : "TMR",

include/target/target_core_base.h

···
 	/* Pointer to transport specific device structure */
 	u32			dev_index;
 	u64			creation_time;
-	u32			num_resets;
-	u64			num_cmds;
-	u64			read_bytes;
-	u64			write_bytes;
-	spinlock_t		stats_lock;
+	atomic_long_t		num_resets;
+	atomic_long_t		num_cmds;
+	atomic_long_t		read_bytes;
+	atomic_long_t		write_bytes;
 	/* Active commands on this virtual SE device */
 	atomic_t		simple_cmds;
 	atomic_t		dev_ordered_id;