Commit df279918 authored Dec 22, 2020 by Jeff Dike Committed by Greg Kroah-Hartman Jan 12, 2021

virtio_net: Fix recursive call to cpus_read_lock()



[ 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: 47be2479 ("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>

parent 586692be

drivers/net/virtio_net.c

+7 −5

Original line number	Original line	Diff line number	Diff line
	@@ -1357,14 +1357,16 @@ static int virtnet_set_channels(struct net_device *dev,

	get_online_cpus();		get_online_cpus();
	err = virtnet_set_queues(vi, queue_pairs);		err = virtnet_set_queues(vi, queue_pairs);
	if (!err) {		if (err) {
	netif_set_real_num_tx_queues(dev, queue_pairs);		put_online_cpus();
	netif_set_real_num_rx_queues(dev, queue_pairs);		goto err;

	virtnet_set_affinity(vi);
	}		}
			virtnet_set_affinity(vi);
	put_online_cpus();		put_online_cpus();

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