From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f45.google.com (mail-pa0-f45.google.com [209.85.220.45]) by kanga.kvack.org (Postfix) with ESMTP id B60C56B0257 for ; Tue, 1 Mar 2016 11:08:17 -0500 (EST) Received: by mail-pa0-f45.google.com with SMTP id fy10so114188126pac.1 for ; Tue, 01 Mar 2016 08:08:17 -0800 (PST) Received: from mail-pf0-f173.google.com (mail-pf0-f173.google.com. [209.85.192.173]) by mx.google.com with ESMTPS id gi2si32472481pac.105.2016.03.01.08.08.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 01 Mar 2016 08:08:17 -0800 (PST) Received: by mail-pf0-f173.google.com with SMTP id 4so36750923pfd.1 for ; Tue, 01 Mar 2016 08:08:17 -0800 (PST) Date: Tue, 1 Mar 2016 17:08:13 +0100 From: Michal Hocko Subject: Re: [PATCH] exit: clear TIF_MEMDIE after exit_task_work Message-ID: <20160301160813.GM9461@dhcp22.suse.cz> References: <1456765329-14890-1-git-send-email-vdavydov@virtuozzo.com> <20160301155212.GJ9461@dhcp22.suse.cz> <20160301175431-mutt-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160301175431-mutt-send-email-mst@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Michael S. Tsirkin" Cc: Vladimir Davydov , Andrew Morton , Tetsuo Handa , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue 01-03-16 17:57:04, Michael S. Tsirkin wrote: > On Tue, Mar 01, 2016 at 04:52:12PM +0100, Michal Hocko wrote: > > [CCing vhost-net maintainer] > > > > On Mon 29-02-16 20:02:09, Vladimir Davydov wrote: > > > An mm_struct may be pinned by a file. An example is vhost-net device > > > created by a qemu/kvm (see vhost_net_ioctl -> vhost_net_set_owner -> > > > vhost_dev_set_owner). > > > > The more I think about that the more I am wondering whether this is > > actually OK and correct. Why does the driver have to pin the address > > space? Nothing really prevents from parallel tearing down of the address > > space anyway so the code cannot expect all the vmas to stay. Would it be > > enough to pin the mm_struct only? > > I'll need to research this. It's a fact that as long as the > device is not stopped, vhost can attempt to access > the address space. But does it expect any specific parts of the address space to be mapped? E.g. proc needs to keep the mm allocated as well for some files but it doesn't pin the address space (mm_users) but rather mm_count (see proc_mem_open). > > I am not sure I understand the code properly but what prevents from > > the situation when a VHOST_SET_OWNER caller dies without calling > > VHOST_RESET_OWNER and so the mm would be pinned indefinitely? > > > > [Keeping the reset of the email for reference] > > We have: > > static const struct file_operations vhost_net_fops = { > .owner = THIS_MODULE, > .release = vhost_net_release, > ... > }; > > When caller dies and after fds are closed, > vhost_net_release calls vhost_dev_cleanup and that > drops the mm reference. Can another process have the device open as well and prevent from destruction? -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org