ext4: fix failure exits

a) leaking root dentry is bad
b) in case of failed ext4_mb_init() we don't want to do ext4_mb_release()
c) OTOH, in the same case we *do* want ext4_ext_release()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ext4/super.c

@@ -3733,10 +3733,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	}
 	if (!S_ISDIR(root->i_mode) || !root->i_blocks || !root->i_size) {
 		ext4_msg(sb, KERN_ERR, "corrupt root inode, run e2fsck");
+		iput(root);
 		goto failed_mount4;
 	}
 	sb->s_root = d_alloc_root(root);
 	if (!sb->s_root) {
+		iput(root);
 		ext4_msg(sb, KERN_ERR, "get root dentry failed");
 		ret = -ENOMEM;
 		goto failed_mount4;
@@ -3773,7 +3775,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	if (err) {
 		ext4_msg(sb, KERN_ERR, "failed to initialize system "
 			 "zone (%d)", err);
-		goto failed_mount4;
+		goto failed_mount4a;
 	}
 
 	ext4_ext_init(sb);
@@ -3830,13 +3832,14 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 failed_mount7:
 	ext4_unregister_li_request(sb);
 failed_mount6:
-	ext4_ext_release(sb);
-failed_mount5:
 	ext4_mb_release(sb);
+failed_mount5:
+	ext4_ext_release(sb);
 	ext4_release_system_zone(sb);
-failed_mount4:
-	iput(root);
+failed_mount4a:
+	dput(sb->s_root);
 	sb->s_root = NULL;
+failed_mount4:
 	ext4_msg(sb, KERN_ERR, "mount failed");
 	destroy_workqueue(EXT4_SB(sb)->dio_unwritten_wq);
 failed_mount_wq: