udf: Fix BUG_ON() in destroy_inode()

udf_clear_inode() can leave behind buffers on mapping's i_private list (when
we truncated preallocation). Call invalidate_inode_buffers() so that the list
is properly cleaned-up before we return from udf_clear_inode(). This is ugly
and suggest that we should cleanup preallocation earlier than in clear_inode()
but currently there's no such call available since drop_inode() is called under
inode lock and thus is unusable for disk operations.
Signed-off-by: Jan Kara <jack@suse.cz>

fs/buffer.c

@@ -878,6 +878,7 @@ void invalidate_inode_buffers(struct inode *inode)
 		spin_unlock(&buffer_mapping->private_lock);
 	}
 }
+EXPORT_SYMBOL(invalidate_inode_buffers);
 
 /*
  * Remove any clean buffers from the inode's buffer list.  This is called

fs/udf/inode.c

@@ -106,6 +106,7 @@ void udf_clear_inode(struct inode *inode)
 		udf_truncate_tail_extent(inode);
 		unlock_kernel();
 		write_inode_now(inode, 0);
+		invalidate_inode_buffers(inode);
 	}
 	iinfo = UDF_I(inode);
 	kfree(iinfo->i_ext.i_data);