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=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 04CAAC65BAF for ; Wed, 12 Dec 2018 10:08:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C6B8720839 for ; Wed, 12 Dec 2018 10:08:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C6B8720839 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727096AbeLLKIh (ORCPT ); Wed, 12 Dec 2018 05:08:37 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48834 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726993AbeLLKIf (ORCPT ); Wed, 12 Dec 2018 05:08:35 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BCE91308428C; Wed, 12 Dec 2018 10:08:35 +0000 (UTC) Received: from jason-ThinkPad-T450s.redhat.com (ovpn-12-55.pek2.redhat.com [10.72.12.55]) by smtp.corp.redhat.com (Postfix) with ESMTP id EB2345C8BC; Wed, 12 Dec 2018 10:08:31 +0000 (UTC) From: Jason Wang To: mst@redhat.com, jasowang@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Tonghao Zhang Subject: [PATCH net V2 2/4] vhost_net: switch to use mutex_trylock() in vhost_net_busy_poll() Date: Wed, 12 Dec 2018 18:08:17 +0800 Message-Id: <20181212100819.21295-3-jasowang@redhat.com> In-Reply-To: <20181212100819.21295-1-jasowang@redhat.com> References: <20181212100819.21295-1-jasowang@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Wed, 12 Dec 2018 10:08:35 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We used to hold the mutex of paired virtqueue in vhost_net_busy_poll(). But this will results an inconsistent lock order which may cause deadlock if we try to bring back the protection of device IOTLB with vq mutex that requires to hold mutex of all virtqueues at the same time. Fix this simply by switching to use mutex_trylock(), when fail just skip the busy polling. This can happen when device IOTLB is under updating which should be rare. Fixes: commit 78139c94dc8c ("net: vhost: lock the vqs one by one") Cc: Tonghao Zhang Signed-off-by: Jason Wang --- drivers/vhost/net.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index ab11b2bee273..ad7a6f475a44 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -513,7 +513,13 @@ static void vhost_net_busy_poll(struct vhost_net *net, struct socket *sock; struct vhost_virtqueue *vq = poll_rx ? tvq : rvq; - mutex_lock_nested(&vq->mutex, poll_rx ? VHOST_NET_VQ_TX: VHOST_NET_VQ_RX); + /* Try to hold the vq mutex of the paired virtqueue. We can't + * use mutex_lock() here since we could not guarantee a + * consistenet lock ordering. + */ + if (!mutex_trylock(&vq->mutex)) + return; + vhost_disable_notify(&net->dev, vq); sock = rvq->private_data; -- 2.17.1