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| author | Michael S. Tsirkin <mst@redhat.com> | 2013-07-09 08:13:04 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2013-07-09 12:45:37 -0700 |
| commit | cbdadbbf0c790f79350a8f36029208944c5487d0 (patch) | |
| tree | 6d63721222da5d652d2e4e65991a15007a83a520 /drivers/net/virtio_net.c | |
| parent | cc229884d3f77ec3b1240e467e0236c3e0647c0c (diff) | |
| download | lwn-cbdadbbf0c790f79350a8f36029208944c5487d0.tar.gz lwn-cbdadbbf0c790f79350a8f36029208944c5487d0.zip | |
virtio_net: fix race in RX VQ processing
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>
Diffstat (limited to 'drivers/net/virtio_net.c')
| -rw-r--r-- | drivers/net/virtio_net.c | 5 |
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); |