virtnet_set_channels can recursively call cpus_read_lock if CONFIG_XPS and CONFIG_HOTPLUG are enabled.

The path is: virtnet_set_channels - calls get_online_cpus(), which is a trivial wrapper around cpus_read_lock() netif_set_real_num_tx_queues netif_reset_xps_queues_gt netif_reset_xps_queues - calls cpus_read_lock()

This call chain and potential deadlock happens when the number of TX queues is reduced.

This commit the removes netif_set_real_num_[tr]x_queues calls from inside the get/put_online_cpus section, as they don't require that it be held.

Signed-off-by: Jeff Dike jdike@akamai.com Acked-by: Jason Wang jasowang@redhat.com Acked-by: Michael S. Tsirkin mst@redhat.com Cc: stable@vger.kernel.org --- drivers/net/virtio_net.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 052975ea0af4..e02c7e0f1cf9 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -2093,14 +2093,16 @@ static int virtnet_set_channels(struct net_device *dev,

get_online_cpus(); err = _virtnet_set_queues(vi, queue_pairs); - if (!err) { - netif_set_real_num_tx_queues(dev, queue_pairs); - netif_set_real_num_rx_queues(dev, queue_pairs); - - virtnet_set_affinity(vi); + if (err){ + put_online_cpus(); + goto err; } + virtnet_set_affinity(vi); put_online_cpus();

+ netif_set_real_num_tx_queues(dev, queue_pairs); + netif_set_real_num_rx_queues(dev, queue_pairs); + err: return err; }