From patchwork Mon Mar 7 18:58:29 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Denis V. Lunev" X-Patchwork-Id: 8521651 Return-Path: X-Original-To: patchwork-qemu-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 47F129F2B4 for ; Mon, 7 Mar 2016 18:59:04 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 975F320254 for ; Mon, 7 Mar 2016 18:59:03 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id ABB3F20218 for ; Mon, 7 Mar 2016 18:59:02 +0000 (UTC) Received: from localhost ([::1]:57744 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ad0Mw-0007Et-1x for patchwork-qemu-devel@patchwork.kernel.org; Mon, 07 Mar 2016 13:59:02 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39134) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ad0Mn-0007DL-Og for qemu-devel@nongnu.org; Mon, 07 Mar 2016 13:58:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ad0Mi-0005nT-Nv for qemu-devel@nongnu.org; Mon, 07 Mar 2016 13:58:53 -0500 Received: from mx2.parallels.com ([199.115.105.18]:43198) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ad0Mi-0005mq-IL for qemu-devel@nongnu.org; Mon, 07 Mar 2016 13:58:48 -0500 Received: from [199.115.105.250] (helo=mail.odin.com) by mx2.parallels.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-SHA384:256) (Exim 4.86) (envelope-from ) id 1ad0MX-0000aa-IC; Mon, 07 Mar 2016 10:58:38 -0800 Received: from [192.168.1.248] (213.251.197.68) by US-EXCH2.sw.swsoft.com (10.255.249.46) with Microsoft SMTP Server (TLS) id 15.0.1130.7; Mon, 7 Mar 2016 10:58:32 -0800 To: "Dr. David Alan Gilbert" , Amit Shah References: <33f7c8c309e6625942e6b8548faa96606a6f99b1.1456212545.git.amit.shah@redhat.com> <20160307124911.GB2253@work-vm> From: "Denis V. Lunev" Message-ID: <56DDCF55.6000203@openvz.org> Date: Mon, 7 Mar 2016 21:58:29 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <20160307124911.GB2253@work-vm> X-ClientProxiedBy: US-EXCH.sw.swsoft.com (10.255.249.47) To US-EXCH2.sw.swsoft.com (10.255.249.46) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 199.115.105.18 Cc: Peter Maydell , Paolo Bonzini , qemu list , Juan Quintela Subject: Re: [Qemu-devel] [PULL 2/5] migration: move bdrv_invalidate_cache_all of of coroutine context X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On 03/07/2016 03:49 PM, Dr. David Alan Gilbert wrote: > * Amit Shah (amit.shah@redhat.com) wrote: >> From: "Denis V. Lunev" >> >> There is a possibility to hit an assert in qcow2_get_specific_info that >> s->qcow_version is undefined. This happens when VM in starting from >> suspended state, i.e. it processes incoming migration, and in the same >> time 'info block' is called. >> >> The problem is that qcow2_invalidate_cache() closes the image and >> memset()s BDRVQcowState in the middle. >> >> The patch moves processing of bdrv_invalidate_cache_all out of >> coroutine context for postcopy migration to avoid that. This function >> is called with the following stack: >> process_incoming_migration_co >> qemu_loadvm_state >> qemu_loadvm_state_main >> loadvm_process_command >> loadvm_postcopy_handle_run >> >> Signed-off-by: Denis V. Lunev >> Tested-by: Dr. David Alan Gilbert > hmm; actually - this segs in a variety of different ways; > there are two problems: > > a) + bh = qemu_bh_new(loadvm_postcopy_handle_run_bh, NULL); > That's the easy one; that NULL should be 'mis', because > the bh is expecting to use it as a MigrationIncomingState > so it segs fairly reliably in the qemu_bh_delete(mis->bh) > > b) The harder problem is that there's a race where qemu_bh_delete > segs, and I'm not 100% sure why yet - it only does it sometime > (i.e. run virt-test and leave it and it occasionally does it). > From the core it looks like qemu->bh is corrupt (0x10101010...) > so maybe mis has been freed at that point? > I'm suspecting this is the postcopy_ram_listen_thread freeing > mis at the end of it, but I don't know yet. > > Dave Yes. this is exactly use-after-free. I have looked into the code and this seems correct. Could you try this simple patch? Den diff --git a/migration/savevm.c b/migration/savevm.c index 96e7db5..9a020ef 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -1446,15 +1446,6 @@ static void *postcopy_ram_listen_thread(void *opaque) migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_ACTIVE, MIGRATION_STATUS_COMPLETED); - /* - * If everything has worked fine, then the main thread has waited - * for us to start, and we're the last use of the mis. - * (If something broke then qemu will have to exit anyway since it's - * got a bad migration state). - */ - migration_incoming_state_destroy(); - - return NULL; } @@ -1533,6 +1524,14 @@ static void loadvm_postcopy_handle_run_bh(void *opaque) } qemu_bh_delete(mis->bh); + + /* + * If everything has worked fine, then the main thread has waited + * for us to start, and we're the last use of the mis. + * (If something broke then qemu will have to exit anyway since it's + * got a bad migration state). + */ + migration_incoming_state_destroy(); } /* After all discards we can start running and asking for pages */