btrfs: properly flag filesystem with BTRFS_FEATURE_INCOMPAT_BIG_METADATA

Commit 6f93e83 seemingly inadvertently moved the code responsible
for flagging the filesystem as having BIG_METADATA to a place where
setting the flag was essentially lost. This means that
filesystems created with kernels containing this bug (starting with 5.15)
can potentially be mounted by older (pre-3.4) kernels. In reality
chances for this happening are low because there are other incompat
flags introduced in the mean time. Still the correct behavior is to set
INCOMPAT_BIG_METADATA flag and persist this in the superblock.

Fixes: 6f93e83 ("btrfs: fix upper limit for max_inline for page size 64K")
CC: [email protected] # 5.4+
Reviewed-by: Qu Wenruo <[email protected]>
Signed-off-by: Nikolay Borisov <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

fs/btrfs/disk-io.c

@@ -3484,16 +3484,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	 */
 	fs_info->compress_type = BTRFS_COMPRESS_ZLIB;
 
-	/*
-	 * Flag our filesystem as having big metadata blocks if they are bigger
-	 * than the page size.
-	 */
-	if (btrfs_super_nodesize(disk_super) > PAGE_SIZE) {
-		if (!(features & BTRFS_FEATURE_INCOMPAT_BIG_METADATA))
-			btrfs_info(fs_info,
-				"flagging fs with big metadata feature");
-		features |= BTRFS_FEATURE_INCOMPAT_BIG_METADATA;
-	}
 
 	/* Set up fs_info before parsing mount options */
 	nodesize = btrfs_super_nodesize(disk_super);
@@ -3534,6 +3524,17 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	if (features & BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA)
 		btrfs_info(fs_info, "has skinny extents");
 
+	/*
+	 * Flag our filesystem as having big metadata blocks if they are bigger
+	 * than the page size.
+	 */
+	if (btrfs_super_nodesize(disk_super) > PAGE_SIZE) {
+		if (!(features & BTRFS_FEATURE_INCOMPAT_BIG_METADATA))
+			btrfs_info(fs_info,
+				"flagging fs with big metadata feature");
+		features |= BTRFS_FEATURE_INCOMPAT_BIG_METADATA;
+	}
+
 	/*
 	 * mixed block groups end up with duplicate but slightly offset
 	 * extent buffers for the same range.  It leads to corruptions