Messages in this thread Patch in this message | | | From | Ben Hutchings <> | Date | Wed, 31 Jul 2013 15:23:09 +0200 | Subject | [28/84] virtio_net: fix race in RX VQ processing |
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3.2.50-rc1 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: Ben Hutchings <ben@decadent.org.uk> --- diff -upr linux-3.2.49/drivers/net/virtio_net.c linux-3.2.49wg/drivers/net/virtio_net.c --- linux-3.2.49/drivers/net/virtio_net.c 2012-01-05 00:55:44.000000000 +0100 +++ linux-3.2.49wg/drivers/net/virtio_net.c 2013-07-27 13:57:33.000000000 +0200 @@ -508,7 +508,7 @@ 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 && @@ -525,8 +525,9 @@ 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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