f2fs: Fix zoned block device support

The introduction of the multi-device feature partially broke the support
for zoned block devices. In the function f2fs_scan_devices, sbi->devs
allocation and initialization is skipped in the case of a single device
mount. This result in no device information structure being allocated
for the device. This is fine if the device is a regular device, but in
the case of a zoned block device, the device zone type array is not
initialized, which causes the function __f2fs_issue_discard_zone to fail
as get_blkz_type is unable to determine the zone type of a section.

Fix this by always allocating and initializing the sbi->devs device
information array even in the case of a single device if that device is
zoned. For this particular case, make sure to obtain a reference on the
single device so that the call to blkdev_put() in destroy_device_list
operates as expected.

Fixes: 3c62be17 ("f2fs: support multiple devices")
Cc: <stable@vger.kernel.org> # v4.10
Signed-off-by: Masato Suzuki <masato.suzuki@wdc.com>
Acked-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -1743,36 +1743,55 @@ int f2fs_commit_super(struct f2fs_sb_info *sbi, bool recover)
 static int f2fs_scan_devices(struct f2fs_sb_info *sbi)
 {
 	struct f2fs_super_block *raw_super = F2FS_RAW_SUPER(sbi);
+	unsigned int max_devices = MAX_DEVICES;
 	int i;
 
-	for (i = 0; i < MAX_DEVICES; i++) {
-		if (!RDEV(i).path[0])
+	/* Initialize single device information */
+	if (!RDEV(0).path[0]) {
+		if (!bdev_is_zoned(sbi->sb->s_bdev))
 			return 0;
+		max_devices = 1;
+	}
 
-		if (i == 0) {
-			sbi->devs = kzalloc(sizeof(struct f2fs_dev_info) *
-						MAX_DEVICES, GFP_KERNEL);
-			if (!sbi->devs)
-				return -ENOMEM;
-		}
+	/*
+	 * Initialize multiple devices information, or single
+	 * zoned block device information.
+	 */
+	sbi->devs = kcalloc(max_devices, sizeof(struct f2fs_dev_info),
+				GFP_KERNEL);
+	if (!sbi->devs)
+		return -ENOMEM;
 
-		memcpy(FDEV(i).path, RDEV(i).path, MAX_PATH_LEN);
-		FDEV(i).total_segments = le32_to_cpu(RDEV(i).total_segments);
-		if (i == 0) {
-			FDEV(i).start_blk = 0;
-			FDEV(i).end_blk = FDEV(i).start_blk +
-				(FDEV(i).total_segments <<
-				sbi->log_blocks_per_seg) - 1 +
-				le32_to_cpu(raw_super->segment0_blkaddr);
-		} else {
-			FDEV(i).start_blk = FDEV(i - 1).end_blk + 1;
-			FDEV(i).end_blk = FDEV(i).start_blk +
-				(FDEV(i).total_segments <<
-				sbi->log_blocks_per_seg) - 1;
-		}
+	for (i = 0; i < max_devices; i++) {
 
-		FDEV(i).bdev = blkdev_get_by_path(FDEV(i).path,
+		if (i > 0 && !RDEV(i).path[0])
+			break;
+
+		if (max_devices == 1) {
+			/* Single zoned block device mount */
+			FDEV(0).bdev =
+				blkdev_get_by_dev(sbi->sb->s_bdev->bd_dev,
 					sbi->sb->s_mode, sbi->sb->s_type);
+		} else {
+			/* Multi-device mount */
+			memcpy(FDEV(i).path, RDEV(i).path, MAX_PATH_LEN);
+			FDEV(i).total_segments =
+				le32_to_cpu(RDEV(i).total_segments);
+			if (i == 0) {
+				FDEV(i).start_blk = 0;
+				FDEV(i).end_blk = FDEV(i).start_blk +
+				    (FDEV(i).total_segments <<
+				    sbi->log_blocks_per_seg) - 1 +
+				    le32_to_cpu(raw_super->segment0_blkaddr);
+			} else {
+				FDEV(i).start_blk = FDEV(i - 1).end_blk + 1;
+				FDEV(i).end_blk = FDEV(i).start_blk +
+					(FDEV(i).total_segments <<
+					sbi->log_blocks_per_seg) - 1;
+			}
+			FDEV(i).bdev = blkdev_get_by_path(FDEV(i).path,
+					sbi->sb->s_mode, sbi->sb->s_type);
+		}
 		if (IS_ERR(FDEV(i).bdev))
 			return PTR_ERR(FDEV(i).bdev);
 
@@ -1792,6 +1811,8 @@ static int f2fs_scan_devices(struct f2fs_sb_info *sbi)
 					"Failed to initialize F2FS blkzone information");
 				return -EINVAL;
 			}
+			if (max_devices == 1)
+				break;
 			f2fs_msg(sbi->sb, KERN_INFO,
 				"Mount Device [%2d]: %20s, %8u, %8x - %8x (zone: %s)",
 				i, FDEV(i).path,