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.
To avoid that, we need to discard the data when the virtqueue is not
ready. udp_buf_sock_to_tap() actually does the same as it reads data
with udp_sock_recv() and if fd_tap is not initialized tap_send_frames()
drops them.
Fixes: 28997fcb29b5 ("vhost-user: add vhost-user")
Link: https://bugs.passt.top/show_bug.cgi?id=185
Signed-off-by: Laurent Vivier
---
Notes:
v2:
- move recvmsg() from udp_vu_sock_to_tap() to udp_vu_sock_recv()
udp_vu.c | 32 ++++++++++++++++++++++----------
1 file changed, 22 insertions(+), 10 deletions(-)
diff --git a/udp_vu.c b/udp_vu.c
index c30dcf97698f..3774d538a2d0 100644
--- a/udp_vu.c
+++ b/udp_vu.c
@@ -65,7 +65,8 @@ static size_t udp_vu_hdrlen(bool v6)
* @v6: Set for IPv6 connections
* @dlen: Size of received data (output)
*
- * Return: number of iov entries used to store the datagram
+ * Return: number of iov entries used to store the datagram, 0 if the datagram
+ * was discarded because the virtqueue is not ready, -1 on error
*/
static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s,
bool v6, ssize_t *dlen)
@@ -77,6 +78,15 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s,
ASSERT(!c->no_udp);
+ if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) {
+ debug("Got UDP packet, but RX virtqueue not usable yet");
+
+ if (recvmsg(s, &msg, MSG_DONTWAIT) < 0)
+ debug_perror("Failed to discard datagram");
+
+ return 0;
+ }
+
/* compute L2 header length */
hdrlen = udp_vu_hdrlen(v6);
@@ -87,7 +97,7 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s,
sizeof(struct virtio_net_hdr_mrg_rxbuf),
NULL);
if (iov_cnt == 0)
- return 0;
+ return -1;
/* reserve space for the headers */
ASSERT(iov_vu[0].iov_len >= MAX(hdrlen, ETH_ZLEN));
@@ -101,7 +111,7 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s,
*dlen = recvmsg(s, &msg, 0);
if (*dlen < 0) {
vu_queue_rewind(vq, iov_cnt);
- return 0;
+ return -1;
}
/* restore the pointer to the headers address */
@@ -216,15 +226,17 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
int iov_used;
iov_used = udp_vu_sock_recv(c, vq, s, v6, &dlen);
- if (iov_used <= 0)
+ if (iov_used < 0)
break;
- udp_vu_prepare(c, toside, dlen);
- if (*c->pcap) {
- udp_vu_csum(toside, iov_used);
- pcap_iov(iov_vu, iov_used,
- sizeof(struct virtio_net_hdr_mrg_rxbuf));
+ if (iov_used > 0) {
+ udp_vu_prepare(c, toside, dlen);
+ if (*c->pcap) {
+ udp_vu_csum(toside, iov_used);
+ pcap_iov(iov_vu, iov_used,
+ sizeof(struct virtio_net_hdr_mrg_rxbuf));
+ }
+ vu_flush(vdev, vq, elem, iov_used);
}
- vu_flush(vdev, vq, elem, iov_used);
}
}
--
2.52.0