nilfs2: allow nilfs_destroy_inode to destroy metadata file inodes

The current nilfs_destroy_inode() doesn't handle metadata file inodes
including gc inodes (dummy inodes used for garbage collection).

This allows nilfs_destroy_inode() to destroy inodes of metadata files.
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/mdt.c

@@ -577,7 +577,5 @@ void nilfs_mdt_destroy(struct inode *inode)
 		nilfs_palloc_destroy_cache(inode);
 	nilfs_mdt_clear(inode);
 
-	kfree(mdi->mi_bgl); /* kfree(NULL) is safe */
-	kfree(mdi);
 	nilfs_destroy_inode(inode);
 }

fs/nilfs2/super.c

@@ -167,6 +167,12 @@ struct inode *nilfs_alloc_inode(struct super_block *sb)
 
 void nilfs_destroy_inode(struct inode *inode)
 {
+	struct nilfs_mdt_info *mdi = NILFS_MDT(inode);
+
+	if (mdi) {
+		kfree(mdi->mi_bgl); /* kfree(NULL) is safe */
+		kfree(mdi);
+	}
 	kmem_cache_free(nilfs_inode_cachep, NILFS_I(inode));
 }