erofs: initialize packed inode after root inode is assigned

As commit 8f7acdae ("staging: erofs: kill all failure handling in
fill_super()"), move the initialization of packed inode after root
inode is assigned, so that the iput() in .put_super() is adequate as
the failure handling.

Otherwise, iput() is also needed in .kill_sb(), in case of the mounting
fails halfway.
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Fixes: b15b2e30 ("erofs: support on-disk compressed fragments data")
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Acked-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230407141710.113882-3-jefflexu@linux.alibaba.comSigned-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/internal.h

@@ -157,6 +157,7 @@ struct erofs_sb_info {
 
 	/* what we really care is nid, rather than ino.. */
 	erofs_nid_t root_nid;
+	erofs_nid_t packed_nid;
 	/* used for statfs, f_files - f_favail */
 	u64 inos;
 

fs/erofs/super.c

@@ -388,17 +388,7 @@ static int erofs_read_superblock(struct super_block *sb)
 #endif
 	sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
 	sbi->root_nid = le16_to_cpu(dsb->root_nid);
-#ifdef CONFIG_EROFS_FS_ZIP
-	sbi->packed_inode = NULL;
-	if (erofs_sb_has_fragments(sbi) && dsb->packed_nid) {
-		sbi->packed_inode =
-			erofs_iget(sb, le64_to_cpu(dsb->packed_nid));
-		if (IS_ERR(sbi->packed_inode)) {
-			ret = PTR_ERR(sbi->packed_inode);
-			goto out;
-		}
-	}
-#endif
+	sbi->packed_nid = le64_to_cpu(dsb->packed_nid);
 	sbi->inos = le64_to_cpu(dsb->inos);
 
 	sbi->build_time = le64_to_cpu(dsb->build_time);
@@ -818,6 +808,16 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 
 	erofs_shrinker_register(sb);
 	/* sb->s_umount is already locked, SB_ACTIVE and SB_BORN are not set */
+#ifdef CONFIG_EROFS_FS_ZIP
+	if (erofs_sb_has_fragments(sbi) && sbi->packed_nid) {
+		sbi->packed_inode = erofs_iget(sb, sbi->packed_nid);
+		if (IS_ERR(sbi->packed_inode)) {
+			err = PTR_ERR(sbi->packed_inode);
+			sbi->packed_inode = NULL;
+			return err;
+		}
+	}
+#endif
 	err = erofs_init_managed_cache(sb);
 	if (err)
 		return err;