Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751722Ab3GHMwb (ORCPT ); Mon, 8 Jul 2013 08:52:31 -0400 Received: from mail-lb0-f173.google.com ([209.85.217.173]:36423 "EHLO mail-lb0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751108Ab3GHMwa (ORCPT ); Mon, 8 Jul 2013 08:52:30 -0400 Message-ID: <51DAB60A.5080305@cogentembedded.com> Date: Mon, 08 Jul 2013 16:52:26 +0400 From: Sergei Shtylyov User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130620 Thunderbird/17.0.7 MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: linux-kernel@vger.kernel.org, Rusty Russell , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: Re: [PATCH 2/2] virtio_net: fix race in RX VQ processing References: <1373274069-4301-1-git-send-email-mst@redhat.com> <1373274069-4301-3-git-send-email-mst@redhat.com> In-Reply-To: <1373274069-4301-3-git-send-email-mst@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1745 Lines: 47 Hello. On 08-07-2013 13:04, Michael S. Tsirkin wrote: > virtio net called virtqueue_enable_cq on RX path after napi_complete, so > with NAPI_STATE_SCHED clear - outside the implicit napi lock. > This violates the requirement to synchronize virtqueue_enable_cq wrt > virtqueue_add_buf. In particular, used event can move backwards, > causing us to lose interrupts. > In a debug build, this can trigger panic within START_USE. > Jason Wang reports that he can trigger the races artificially, > by adding udelay() in virtqueue_enable_cb() after virtio_mb(). > However, we must call napi_complete to clear NAPI_STATE_SCHED before > polling the virtqueue for used buffers, otherwise napi_schedule_prep in > a callback will fail, causing us to lose RX events. > To fix, call virtqueue_enable_cb_prepare with NAPI_STATE_SCHED > set (under napi lock), later call virtqueue_poll with > NAPI_STATE_SCHED clear (outside the lock). > Reported-by: Jason Wang > Signed-off-by: Michael S. Tsirkin > --- > drivers/net/virtio_net.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 5305bd1..fbdd79a 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -622,8 +622,9 @@ again: > > /* Out of packets? */ > if (received < budget) { > + unsigned r = virtqueue_enable_cb_prepare(rq->vq); Empty line wouldn't hurt here, after declaration. WBR, Sergei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/