From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=38681 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1P9Ck5-0001vt-Tz for qemu-devel@nongnu.org; Fri, 22 Oct 2010 04:12:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1P9Chn-0008AH-IB for qemu-devel@nongnu.org; Fri, 22 Oct 2010 04:10:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:28043) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1P9Chn-00089i-Ar for qemu-devel@nongnu.org; Fri, 22 Oct 2010 04:10:27 -0400 Date: Fri, 22 Oct 2010 09:10:16 +0100 From: "Daniel P. Berrange" Subject: Re: [Qemu-devel] [PATCH 2/2] v2 Fix Block Hotplug race with drive_unplug() Message-ID: <20101022081016.GB14920@redhat.com> References: <1287498749-10400-1-git-send-email-ryanh@us.ibm.com> <1287498749-10400-3-git-send-email-ryanh@us.ibm.com> <20101021132738.GM27578@redhat.com> <20101021213746.GK22904@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101021213746.GK22904@us.ibm.com> Reply-To: "Daniel P. Berrange" List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ryan Harper Cc: Stefan Hajnoczi , Anthony Liguori , qemu-devel@nongnu.org, Kevin Wolf On Thu, Oct 21, 2010 at 04:37:46PM -0500, Ryan Harper wrote: > * Daniel P. Berrange [2010-10-21 08:29]: > > On Tue, Oct 19, 2010 at 09:32:29AM -0500, Ryan Harper wrote: > > > Block hot unplug is racy since the guest is required to acknowlege the ACPI > > > unplug event; this may not happen synchronously with the device removal command > > > > > > This series aims to close a gap where by mgmt applications that assume the > > > block resource has been removed without confirming that the guest has > > > acknowledged the removal may re-assign the underlying device to a second guest > > > leading to data leakage. > > > > > > This series introduces a new montor command to decouple asynchornous device > > > removal from restricting guest access to a block device. We do this by creating > > > a new monitor command drive_unplug which maps to a bdrv_unplug() command which > > > does a qemu_aio_flush; bdrv_flush() and bdrv_close(). Once complete, subsequent > > > IO is rejected from the device and the guest will get IO errors but continue to > > > function. > > > > > > A subsequent device removal command can be issued to remove the device, to which > > > the guest may or maynot respond, but as long as the unplugged bit is set, no IO > > > will be sumbitted. > > > > The name 'drive_unplug' suggests to me that the drive object is > > not being deleted/free()d ? Is that correct understanding, and if > > so, what is responsible for finally free()ing the drive backend ? > > It's technically the BlockDriverState Driver that we're closing. To > fully release the remaining resources, a device_del is required (which > of course requires guest participation with the current > interface). > > Once QEMU issues the removal request, the guest responds and the piix4 > acpi handler for pciej_write writes invokes qdev_free() on the target > device. qdev_free() on the pci device will make it's way to the qdev > exit handler registered for virtio-blk devices, virtio_blk_exit_pci(). > virtio_blk_exit_pci() marks the drive structure for deletion. When qdev > calls the properties handler, it invokes free_drive() on the disk and > that calls blockdev_auto_del() which will do a bdrv_delete() which nukes > the remaining objects (the acutal BlockDriverState). > > I think I got the whole path in there. Ok, thanks, that makes sense to me. Sounds like we do still need a separate drive_del in the future to handle the different case of, drive_add, followed by a device_add attempt which fails. Regards, Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|