Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [ 38/39] virtio_net: fix race in RX VQ processing | Date | Fri, 2 Aug 2013 18:18:48 +0800 |
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3.4-stable review patch. If anyone has any objections, please let me know.
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From: Michael S. Tsirkin <mst@redhat.com>
commit cbdadbbf0c790f79350a8f36029208944c5487d0 upstream
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> [wg: Backported to 3.2] Signed-off-by: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- --- drivers/net/virtio_net.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -518,7 +518,7 @@ static int virtnet_poll(struct napi_stru { struct virtnet_info *vi = container_of(napi, struct virtnet_info, napi); void *buf; - unsigned int len, received = 0; + unsigned int r, len, received = 0; again: while (received < budget && @@ -535,8 +535,9 @@ again: /* Out of packets? */ if (received < budget) { + r = virtqueue_enable_cb_prepare(vi->rvq); napi_complete(napi); - if (unlikely(!virtqueue_enable_cb(vi->rvq)) && + if (unlikely(virtqueue_poll(vi->rvq, r)) && napi_schedule_prep(napi)) { virtqueue_disable_cb(vi->rvq); __napi_schedule(napi);
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