Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752364Ab3GID2r (ORCPT ); Mon, 8 Jul 2013 23:28:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51715 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751026Ab3GID2q (ORCPT ); Mon, 8 Jul 2013 23:28:46 -0400 Message-ID: <51DB8362.4020405@redhat.com> Date: Tue, 09 Jul 2013 11:28:34 +0800 From: Jason Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130623 Thunderbird/17.0.7 MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, virtualization@lists.linux-foundation.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 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1989 Lines: 49 On 07/08/2013 05:04 PM, 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 > --- Tested-by: Jason Wang Acked-by: Jason Wang > 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); > napi_complete(napi); > - if (unlikely(!virtqueue_enable_cb(rq->vq)) && > + if (unlikely(virtqueue_poll(rq->vq, r)) && > napi_schedule_prep(napi)) { > virtqueue_disable_cb(rq->vq); > __napi_schedule(napi); -- 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/