[PATCH 5.10 017/145] virtio_net: Fix recursive call to cpus_read_lock()

Greg Kroah-Hartman
2021-01-11T13:14:37Z

From: Jeff Dike <jdike@akamai.com>

[ Upstream commit de33212f768c5d9e2fe791b008cb26f92f0aa31c ]

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.

Fixes: 47be24796c13 ("virtio-net: fix the set affinity bug when CPU IDs are not consecutive")
Signed-off-by: Jeff Dike <jdike@akamai.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/20201223025421.671-1-jdike@akamai.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/virtio_net.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2093,14 +2093,16 @@ static int virtnet_set_channels(struct n

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;
}