From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759983Ab3GaN0d (ORCPT ); Wed, 31 Jul 2013 09:26:33 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:47094 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759854Ab3GaN0I (ORCPT ); Wed, 31 Jul 2013 09:26:08 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Jason Wang" , "Michael S. Tsirkin" , "Wolfram Gloger" , "David S. Miller" Date: Wed, 31 Jul 2013 15:23:09 +0200 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [28/84] virtio_net: fix race in RX VQ processing In-Reply-To: X-SA-Exim-Connect-IP: 151.216.67.181 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.50-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Michael S. Tsirkin commit cbdadbbf0c790f79350a8f36029208944c5487d0 upstream. 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 [wg: Backported to 3.2] Signed-off-by: Wolfram Gloger Signed-off-by: Ben Hutchings --- diff -upr linux-3.2.49/drivers/net/virtio_net.c linux-3.2.49wg/drivers/net/virtio_net.c --- linux-3.2.49/drivers/net/virtio_net.c 2012-01-05 00:55:44.000000000 +0100 +++ linux-3.2.49wg/drivers/net/virtio_net.c 2013-07-27 13:57:33.000000000 +0200 @@ -508,7 +508,7 @@ static int virtnet_poll(struct napi_stru { 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 && @@ -525,8 +525,9 @@ 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);