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authorMichael S. Tsirkin <mst@redhat.com>2013-07-09 08:13:04 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-07-28 16:29:56 -0700
commit2b0e8a4ff83fd85afe5d0b84a2e1c6faa5fa56b8 (patch)
tree797347db0c30e89ff3fbb442e69cac79e1e5d269 /drivers/net
parentc23b1ece6112ed0f227fdc881db33c6427b65222 (diff)
virtio_net: fix race in RX VQ processing
[ Upstream commit cbdadbbf0c790f79350a8f36029208944c5487d0 ] 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 <jasowang@redhat.com> Tested-by: Jason Wang <jasowang@redhat.com> Acked-by: Jason Wang <jasowang@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/net')
-rw-r--r--drivers/net/virtio_net.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c9e00387d999..42d670a468f8 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -602,7 +602,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
container_of(napi, struct receive_queue, napi);
struct virtnet_info *vi = rq->vq->vdev->priv;
void *buf;
- unsigned int len, received = 0;
+ unsigned int r, len, received = 0;
again:
while (received < budget &&
@@ -619,8 +619,9 @@ again:
/* Out of packets? */
if (received < budget) {
+ r = virtqueue_enable_cb_prepare(rq->vq);
napi_complete(napi);
- if (unlikely(!virtqueue_enable_cb(rq->vq)) &&
+ if (unlikely(virtqueue_poll(rq->vq, r)) &&
napi_schedule_prep(napi)) {
virtqueue_disable_cb(rq->vq);
__napi_schedule(napi);