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 BB36FC6786C for ; Thu, 13 Dec 2018 02:53:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C79F20873 for ; Thu, 13 Dec 2018 02:53:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C79F20873 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 S1726923AbeLMCx4 (ORCPT ); Wed, 12 Dec 2018 21:53:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:38280 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726858AbeLMCxw (ORCPT ); Wed, 12 Dec 2018 21:53:52 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7AF4A80F93; Thu, 13 Dec 2018 02:53:52 +0000 (UTC) Received: from jason-ThinkPad-T450s.redhat.com (ovpn-12-167.pek2.redhat.com [10.72.12.167]) by smtp.corp.redhat.com (Postfix) with ESMTP id C44C15D70A; Thu, 13 Dec 2018 02:53:49 +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 V3 2/3] vhost_net: switch to use mutex_trylock() in vhost_net_busy_poll() Date: Thu, 13 Dec 2018 10:53:38 +0800 Message-Id: <20181213025339.14023-3-jasowang@redhat.com> In-Reply-To: <20181213025339.14023-1-jasowang@redhat.com> References: <20181213025339.14023-1-jasowang@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Thu, 13 Dec 2018 02:53:52 +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 Acked-by: Michael S. Tsirkin 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