From 27fe2c366213592a862d8f5160c606eded3947c7 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Sun, 4 Aug 2013 15:43:40 +0800 Subject: virtio_net: fix race in RX VQ processing 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: Greg Kroah-Hartman --- drivers/net/virtio_net.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'drivers') diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index f6853247a620..316a565fb9e4 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -480,7 +480,7 @@ 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 && @@ -497,8 +497,9 @@ 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); -- cgit v1.2.3