Patch "scsi: sd: Do not override max_sectors_kb sysfs setting" has been added to the 4.13-stable tree

@@ -3109,8 +3109,6 @@ static int sd_revalidate_disk(struct gen
 		sd_read_security(sdkp, buffer);
 	}
 
-	sdkp->first_scan = 0;
-
 	/*
 	 * We now have all cache related info, determine how we deal
 	 * with flush requests.

@@ -3125,7 +3123,7 @@ static int sd_revalidate_disk(struct gen
 	q->limits.max_dev_sectors = logical_to_sectors(sdp, dev_max);
 
 	/*
-	 * Use the device's preferred I/O size for reads and writes
+	 * Determine the device's preferred I/O size for reads and writes
 	 * unless the reported value is unreasonably small, large, or
 	 * garbage.
 	 */

@@ -3139,8 +3137,19 @@ static int sd_revalidate_disk(struct gen
 		rw_max = min_not_zero(logical_to_sectors(sdp, dev_max),
 				      (sector_t)BLK_DEF_MAX_SECTORS);
 
-	/* Combine with controller limits */
-	q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q));
+	/* Do not exceed controller limit */
+	rw_max = min(rw_max, queue_max_hw_sectors(q));
+
+	/*
+	 * Only update max_sectors if previously unset or if the current value
+	 * exceeds the capabilities of the hardware.
+	 */
+	if (sdkp->first_scan ||
+	    q->limits.max_sectors > q->limits.max_dev_sectors ||
+	    q->limits.max_sectors > q->limits.max_hw_sectors)
+		q->limits.max_sectors = rw_max;
+
+	sdkp->first_scan = 0;
 
 	set_capacity(disk, logical_to_sectors(sdp, sdkp->capacity));
 	sd_config_write_same(sdkp);