5.4-stable review patch. If anyone has any objections, please let me know.
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From: Ilya Maximets i.maximets@ovn.org
commit 47e55e4b410f7d552e43011baa5be1aab4093990 upstream.
Commit in a fixes tag attempted to fix the issue in the following sequence of calls:
do_output -> ovs_vport_send -> dev_queue_xmit -> __dev_queue_xmit -> netdev_core_pick_tx -> skb_tx_hash
When device is unregistering, the 'dev->real_num_tx_queues' goes to zero and the 'while (unlikely(hash >= qcount))' loop inside the 'skb_tx_hash' becomes infinite, locking up the core forever.
But unfortunately, checking just the carrier status is not enough to fix the issue, because some devices may still be in unregistering state while reporting carrier status OK.
One example of such device is a net/dummy. It sets carrier ON on start, but it doesn't implement .ndo_stop to set the carrier off. And it makes sense, because dummy doesn't really have a carrier. Therefore, while this device is unregistering, it's still easy to hit the infinite loop in the skb_tx_hash() from the OVS datapath. There might be other drivers that do the same, but dummy by itself is important for the OVS ecosystem, because it is frequently used as a packet sink for tcpdump while debugging OVS deployments. And when the issue is hit, the only way to recover is to reboot.
Fix that by also checking if the device is running. The running state is handled by the net core during unregistering, so it covers unregistering case better, and we don't really need to send packets to devices that are not running anyway.
While only checking the running state might be enough, the carrier check is preserved. The running and the carrier states seem disjoined throughout the code and different drivers. And other core functions like __dev_direct_xmit() check both before attempting to transmit a packet. So, it seems safer to check both flags in OVS as well.
Fixes: 066b86787fa3 ("net: openvswitch: fix race on port output") Reported-by: Friedrich Weber f.weber@proxmox.com Closes: https://mail.openvswitch.org/pipermail/ovs-discuss/2025-January/053423.html Signed-off-by: Ilya Maximets i.maximets@ovn.org Tested-by: Friedrich Weber f.weber@proxmox.com Reviewed-by: Aaron Conole aconole@redhat.com Link: https://patch.msgid.link/20250109122225.4034688-1-i.maximets@ovn.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Carlos Soto carlos.soto@broadcom.com Signed-off-by: Florian Fainelli florian.fainelli@broadcom.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/openvswitch/actions.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/net/openvswitch/actions.c +++ b/net/openvswitch/actions.c @@ -920,7 +920,9 @@ static void do_output(struct datapath *d { struct vport *vport = ovs_vport_rcu(dp, out_port);
- if (likely(vport && netif_carrier_ok(vport->dev))) { + if (likely(vport && + netif_running(vport->dev) && + netif_carrier_ok(vport->dev))) { u16 mru = OVS_CB(skb)->mru; u32 cutlen = OVS_CB(skb)->cutlen;