From 7ebc79037c5f426bfb08cc506670bf7dd3912430 Mon Sep 17 00:00:00 2001 From: Tom Lendacky Date: Mon, 8 Feb 2010 10:10:01 -0600 Subject: [PATCH] virtio-net: fix network stall under load Fix a race condition where qemu finds that there are not enough virtio ring buffers available and the guest make more buffers available before qemu can enable notifications. Signed-off-by: Tom Lendacky Signed-off-by: Anthony Liguori (cherry picked from commit 06b1297017415ae6a07a0e97ad7d8e90b2d95823) --- hw/virtio-net.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/hw/virtio-net.c b/hw/virtio-net.c index 2f201ffc7..d8a1629dc 100644 --- a/hw/virtio-net.c +++ b/hw/virtio-net.c @@ -384,7 +384,15 @@ static int virtio_net_has_buffers(VirtIONet *n, int bufsize) (n->mergeable_rx_bufs && !virtqueue_avail_bytes(n->rx_vq, bufsize, 0))) { virtio_queue_set_notification(n->rx_vq, 1); - return 0; + + /* To avoid a race condition where the guest has made some buffers + * available after the above check but before notification was + * enabled, check for available buffers again. + */ + if (virtio_queue_empty(n->rx_vq) || + (n->mergeable_rx_bufs && + !virtqueue_avail_bytes(n->rx_vq, bufsize, 0))) + return 0; } virtio_queue_set_notification(n->rx_vq, 0); -- 2.39.2