From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A84A4CA90AF for ; Wed, 13 May 2020 09:40:56 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6E218206B8 for ; Wed, 13 May 2020 09:40:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b="eotdw6WQ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6E218206B8 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=yandex-team.ru Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:53430 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jYnsl-0006oA-J3 for qemu-devel@archiver.kernel.org; Wed, 13 May 2020 05:40:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42412) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jYnrl-0006Av-Mp; Wed, 13 May 2020 05:39:53 -0400 Received: from forwardcorp1p.mail.yandex.net ([2a02:6b8:0:1472:2741:0:8b6:217]:38960) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jYnrk-0000U4-7H; Wed, 13 May 2020 05:39:53 -0400 Received: from mxbackcorp2j.mail.yandex.net (mxbackcorp2j.mail.yandex.net [IPv6:2a02:6b8:0:1619::119]) by forwardcorp1p.mail.yandex.net (Yandex) with ESMTP id 143302E1563; Wed, 13 May 2020 12:39:49 +0300 (MSK) Received: from iva4-7c3d9abce76c.qloud-c.yandex.net (iva4-7c3d9abce76c.qloud-c.yandex.net [2a02:6b8:c0c:4e8e:0:640:7c3d:9abc]) by mxbackcorp2j.mail.yandex.net (mxbackcorp/Yandex) with ESMTP id UCec00BROG-djoSIdUx; Wed, 13 May 2020 12:39:49 +0300 Precedence: bulk DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1589362789; bh=Y/7niz3DsV0Kmn2cneECuqjP3Mq88FjyLqh/oS6YG+M=; h=In-Reply-To:Message-ID:Subject:To:From:References:Date:Cc; b=eotdw6WQDXaJeGNBZUWnDIdK2iGSuIuEhMmAKL1hhGKX6WyXNL3bGUiHE18Czp6tW ECPuDArVj8PgsMeW1C3yr0b3tkZYrwUvIc23Ygcg/m/iECCzi2fmGQ/Ee+KocyePVF 268KW6puleGZYl3iNU0nCuOKrMu/poy8QQuNOgc4= Authentication-Results: mxbackcorp2j.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Received: from dynamic-vpn.dhcp.yndx.net (dynamic-vpn.dhcp.yndx.net [2a02:6b8:b081:324::1:5]) by iva4-7c3d9abce76c.qloud-c.yandex.net (smtpcorp/Yandex) with ESMTPSA id PA8DqTqyDp-diWefuRf; Wed, 13 May 2020 12:39:45 +0300 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client certificate not present) Date: Wed, 13 May 2020 12:39:43 +0300 From: Dima Stepanov To: Jason Wang Subject: Re: [PATCH v2 5/5] vhost: add device started check in migration set log Message-ID: <20200513093934.GA15883@dimastep-nix> References: <20200511092541.GA27558@dimastep-nix> <20200512093521.GA5363@dimastep-nix> <5afd8f14-ed9f-d3e1-3e7f-649a5140db28@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5afd8f14-ed9f-d3e1-3e7f-649a5140db28@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Received-SPF: pass client-ip=2a02:6b8:0:1472:2741:0:8b6:217; envelope-from=dimastep@yandex-team.ru; helo=forwardcorp1p.mail.yandex.net X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/13 05:39:49 X-ACL-Warn: Detected OS = ??? X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: fam@euphon.net, kwolf@redhat.com, stefanha@redhat.com, qemu-block@nongnu.org, mst@redhat.com, qemu-devel@nongnu.org, dgilbert@redhat.com, arei.gonglei@huawei.com, fengli@smartx.com, yc-core@yandex-team.ru, pbonzini@redhat.com, marcandre.lureau@redhat.com, raphael.norwitz@nutanix.com, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, May 13, 2020 at 11:20:50AM +0800, Jason Wang wrote: > > On 2020/5/12 下午5:35, Dima Stepanov wrote: > >On Tue, May 12, 2020 at 11:32:50AM +0800, Jason Wang wrote: > >>On 2020/5/11 下午5:25, Dima Stepanov wrote: > >>>On Mon, May 11, 2020 at 11:15:53AM +0800, Jason Wang wrote: > >>>>On 2020/4/30 下午9:36, Dima Stepanov wrote: > >>>>>If vhost-user daemon is used as a backend for the vhost device, then we > >>>>>should consider a possibility of disconnect at any moment. If such > >>>>>disconnect happened in the vhost_migration_log() routine the vhost > >>>>>device structure will be clean up. > >>>>>At the start of the vhost_migration_log() function there is a check: > >>>>> if (!dev->started) { > >>>>> dev->log_enabled = enable; > >>>>> return 0; > >>>>> } > >>>>>To be consistent with this check add the same check after calling the > >>>>>vhost_dev_set_log() routine. This in general help not to break a > >>>>>migration due the assert() message. But it looks like that this code > >>>>>should be revised to handle these errors more carefully. > >>>>> > >>>>>In case of vhost-user device backend the fail paths should consider the > >>>>>state of the device. In this case we should skip some function calls > >>>>>during rollback on the error paths, so not to get the NULL dereference > >>>>>errors. > >>>>> > >>>>>Signed-off-by: Dima Stepanov > >>>>>--- > >>>>> hw/virtio/vhost.c | 39 +++++++++++++++++++++++++++++++++++---- > >>>>> 1 file changed, 35 insertions(+), 4 deletions(-) > >>>>> > >>>>>diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > >>>>>index 3ee50c4..d5ab96d 100644 > >>>>>--- a/hw/virtio/vhost.c > >>>>>+++ b/hw/virtio/vhost.c > >>>>>@@ -787,6 +787,17 @@ static int vhost_dev_set_features(struct vhost_dev *dev, > >>>>> static int vhost_dev_set_log(struct vhost_dev *dev, bool enable_log) > >>>>> { > >>>>> int r, i, idx; > >>>>>+ > >>>>>+ if (!dev->started) { > >>>>>+ /* > >>>>>+ * If vhost-user daemon is used as a backend for the > >>>>>+ * device and the connection is broken, then the vhost_dev > >>>>>+ * structure will be reset all its values to 0. > >>>>>+ * Add additional check for the device state. > >>>>>+ */ > >>>>>+ return -1; > >>>>>+ } > >>>>>+ > >>>>> r = vhost_dev_set_features(dev, enable_log); > >>>>> if (r < 0) { > >>>>> goto err_features; > >>>>>@@ -801,12 +812,19 @@ static int vhost_dev_set_log(struct vhost_dev *dev, bool enable_log) > >>>>> } > >>>>> return 0; > >>>>> err_vq: > >>>>>- for (; i >= 0; --i) { > >>>>>+ /* > >>>>>+ * Disconnect with the vhost-user daemon can lead to the > >>>>>+ * vhost_dev_cleanup() call which will clean up vhost_dev > >>>>>+ * structure. > >>>>>+ */ > >>>>>+ for (; dev->started && (i >= 0); --i) { > >>>>> idx = dev->vhost_ops->vhost_get_vq_index( > >>>>Why need the check of dev->started here, can started be modified outside > >>>>mainloop? If yes, I don't get the check of !dev->started in the beginning of > >>>>this function. > >>>> > >>>No dev->started can't change outside the mainloop. The main problem is > >>>only for the vhost_user_blk daemon. Consider the case when we > >>>successfully pass the dev->started check at the beginning of the > >>>function, but after it we hit the disconnect on the next call on the > >>>second or third iteration: > >>> r = vhost_virtqueue_set_addr(dev, dev->vqs + i, idx, enable_log); > >>>The unix socket backend device will call the disconnect routine for this > >>>device and reset the structure. So the structure will be reset (and > >>>dev->started set to false) inside this set_addr() call. > >>I still don't get here. I think the disconnect can not happen in the middle > >>of vhost_dev_set_log() since both of them were running in mainloop. And even > >>if it can, we probably need other synchronization mechanism other than > >>simple check here. > >Disconnect isn't happened in the separate thread it is happened in this > >routine inside vhost_dev_set_log. When for instance vhost_user_write() > >call failed: > > vhost_user_set_log_base() > > vhost_user_write() > > vhost_user_blk_disconnect() > > vhost_dev_cleanup() > > vhost_user_backend_cleanup() > >So the point is that if we somehow got a disconnect with the > >vhost-user-blk daemon before the vhost_user_write() call then it will > >continue clean up by running vhost_user_blk_disconnect() function. I > >wrote a more detailed backtrace stack in the separate thread, which is > >pretty similar to what we have here: > > Re: [PATCH v2 4/5] vhost: check vring address before calling unmap > >The places are different but the problem is pretty similar. > > > Yes. > > > > > >So if vhost-user commands handshake then everything is fine and > >reconnect will work as expected. The only problem is how to handle > >reconnect properly between vhost-user command send/receive. > > > >As i wrote we have a test: > > - run src VM with vhost-usr-blk daemon used > > - run fio inside it > > - perform reconnect every X seconds (just kill and restart daemon), > > X is random > > - run dst VM > > - perform migration > > - fio should complete in dst VM > >And we cycle this test like forever. > >So it fails once per ~25 iteration. By adding some delays inside qemu we > >were able to make the race window larger. > > > It would be better if we can draft some qtest for this. Yes, i'm in process of figuring out how to make/reproduce it in the qtest framework instead of our internal one. > > Thanks > > > > >