From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:58846 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726885AbeIQUwR (ORCPT ); Mon, 17 Sep 2018 16:52:17 -0400 Date: Mon, 17 Sep 2018 17:24:24 +0200 From: Oleg Nesterov To: "Eric W. Biederman" Cc: Jeff Layton , viro@zeniv.linux.org.uk, berrange@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [PATCH v3 1/3] exec: separate thread_count for files_struct Message-ID: <20180917152424.GA25173@redhat.com> References: <20180914105310.6454-1-jlayton@kernel.org> <20180914105310.6454-2-jlayton@kernel.org> <20180915160423.GA31461@redhat.com> <87o9cxv2wh.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87o9cxv2wh.fsf@xmission.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 09/16, Eric W. Biederman wrote: > > Oleg Nesterov writes: > > > As for binder.c, in this case we probably actually want to unshare ->files > > on exec so we can ignore it? > > Looking at the binder case it only captures ->files on mmap. Exec > ditches the mmap. So if the order of operations are correct than > the dropping of the old mm will also drop the count on files_struct > held by binder. > > So semantically binder should not effect locks on exec, Agreed, but it does. Before your "[PATCH 0/3] exec: Moving unshare_files_struct" unshare_files() is called before exec_mmap(). And even with this series we can have another CLONE_VM process. Howver, I think this doesn't really matter. binder does __fd_install(files), so if it actually has a reference to execing_task->files, I think it should be unshared anyway. > In short as long as we get the oder of operations correct we should be > able to safely ignore binder, and not have binder affect the results of > this code. Agreed. Oleg.