Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751862Ab3GJEj6 (ORCPT ); Wed, 10 Jul 2013 00:39:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:6567 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751061Ab3GJEj4 (ORCPT ); Wed, 10 Jul 2013 00:39:56 -0400 Date: Wed, 10 Jul 2013 12:39:53 +0800 From: Asias He To: Jason Wang Cc: "Michael S. Tsirkin" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH 2/2] virtio_net: fix race in RX VQ processing Message-ID: <20130710043953.GB5962@hj.localdomain> References: <1373274069-4301-1-git-send-email-mst@redhat.com> <1373274069-4301-3-git-send-email-mst@redhat.com> <51DB8362.4020405@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51DB8362.4020405@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2380 Lines: 60 On Tue, Jul 09, 2013 at 11:28:34AM +0800, Jason Wang wrote: > 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 Acked-by: Asias He > > --- > > 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); > > _______________________________________________ > Virtualization mailing list > Virtualization@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/virtualization -- Asias -- 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/