Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752517Ab3GHJDc (ORCPT ); Mon, 8 Jul 2013 05:03:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:6980 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751997Ab3GHJDa (ORCPT ); Mon, 8 Jul 2013 05:03:30 -0400 Date: Mon, 8 Jul 2013 12:04:41 +0300 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Rusty Russell , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: [PATCH 2/2] virtio_net: fix race in RX VQ processing Message-ID: <1373274069-4301-3-git-send-email-mst@redhat.com> References: <1373274069-4301-1-git-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1373274069-4301-1-git-send-email-mst@redhat.com> X-Mutt-Fcc: =sent Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1786 Lines: 47 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); 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); -- MST -- 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/