On Tue, 22 Dec 2020 11:49:04 +0800 Jason Wang wrote:

On 2020/12/22 上午11:36, Jeff Dike wrote:

quoted

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 <redacted>

Adding netdev.

The patch can go with -net and is needed for -stable.

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks, we'll need a repost with netdev CCed to apply it to net, 
I don't have this one in my inbox or in patchwork.

Jeff please make sure to keep the acks when reposting.