[PATCH] udp_vu: Discard datagrams when RX virtqueue is not usable

During vhost-user device initialization, UDP datagrams may arrive on listening sockets before the guest has enabled the RX virtqueue. When this happens, udp_vu_sock_recv() returns 0 without consuming the datagram from the socket. The caller, udp_sock_fwd(), uses a while loop with udp_peek_addr() to process pending datagrams. Since the datagram remains in the socket buffer, udp_peek_addr() keeps returning data available, causing a busy loop with 100% CPU usage. Add an early check for virtqueue readiness in udp_vu_sock_to_tap(), mirroring tcp_vu_data_from_sock(). When the queue is not enabled or not started, explicitly discard the datagram with recvmsg() and return. The caller will drain remaining datagrams through repeated calls. Fixes: 28997fcb29b5 ("vhost-user: add vhost-user") Link: https://bugs.passt.top/show_bug.cgi?id=185 Signed-off-by: Laurent Vivier --- udp_vu.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/udp_vu.c b/udp_vu.c index c30dcf97698f..67f4ee619bfb 100644 --- a/udp_vu.c +++ b/udp_vu.c @@ -211,6 +211,17 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx) struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE]; int i; + if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) { + struct msghdr msg = { 0 }; + + debug("Got UDP packet, but RX virtqueue not usable yet"); + + if (recvmsg(s, &msg, MSG_DONTWAIT) < 0) + debug_perror("Failed to discard datagram"); + + return; + } + for (i = 0; i < n; i++) { ssize_t dlen; int iov_used; -- 2.52.0