From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754652Ab3IKEa0 (ORCPT ); Wed, 11 Sep 2013 00:30:26 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:3623 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752951Ab3IKE3F (ORCPT ); Wed, 11 Sep 2013 00:29:05 -0400 X-Authority-Analysis: v=2.0 cv=V4T/IJbi c=1 sm=0 a=Sro2XwOs0tJUSHxCKfOySw==:17 a=Drc5e87SC40A:10 a=Ciwy3NGCPMMA:10 a=ulkYN_iQIDMA:10 a=5SG0PmZfjMsA:10 a=bbbx4UPp9XUA:10 a=meVymXHHAAAA:8 a=KGjhK52YXX0A:10 a=mAe00Se35yEA:10 a=20KFwNOVAAAA:8 a=J1Y8HTJGAAAA:8 a=wAwfuhEyL-vLSwEzO4gA:9 a=jEp0ucaQiEUA:10 a=4N9Db7Z2_RYA:10 a=jeBq3FmKZ4MA:10 a=wd9KZIgbKDeiVy_P:21 a=BB7zgHEgxMRP9X95:21 a=Sro2XwOs0tJUSHxCKfOySw==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 67.255.60.225 Message-Id: <20130911042859.834349673@goodmis.org> User-Agent: quilt/0.60-1 Date: Wed, 11 Sep 2013 00:27:52 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Jason Wang , "Michael S. Tsirkin" , "David S. Miller" Subject: [045/251] virtio_net: fix race in RX VQ processing References: <20130911042707.738353451@goodmis.org> Content-Disposition: inline; filename=0045-virtio_net-fix-race-in-RX-VQ-processing.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.6.11.9-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: "Michael S. Tsirkin" [ Upstream commit cbdadbbf0c790f79350a8f36029208944c5487d0 ] 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 Tested-by: Jason Wang Acked-by: Jason Wang Signed-off-by: Michael S. Tsirkin Signed-off-by: David S. Miller Signed-off-by: Steven Rostedt --- drivers/net/virtio_net.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 83d2b0c..fc04222 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -528,7 +528,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget) { struct virtnet_info *vi = container_of(napi, struct virtnet_info, napi); void *buf; - unsigned int len, received = 0; + unsigned int r, len, received = 0; again: while (received < budget && @@ -545,8 +545,9 @@ again: /* Out of packets? */ if (received < budget) { + r = virtqueue_enable_cb_prepare(vi->rvq); napi_complete(napi); - if (unlikely(!virtqueue_enable_cb(vi->rvq)) && + if (unlikely(virtqueue_poll(vi->rvq, r)) && napi_schedule_prep(napi)) { virtqueue_disable_cb(vi->rvq); __napi_schedule(napi); -- 1.7.10.4