[Bug 219703] System freeze when creating bridge over vlan over lagg over ixgbe

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=219703

            Bug ID: 219703
           Summary: System freeze when creating bridge over vlan over lagg
                    over ixgbe
           Product: Base System
           Version: 11.0-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: topical at gmx.net

I have an Intel 82599ES card, using standard ixgbe driver (no special
parameters). The two ports are combined into a lagg. For virtual machines, a
vlan is created on the lagg. This vlan is connected to a bridge. behyve
machines shall be connected to this bridge. In my case, there are 3 vlans and
bridges, but the problem occurs already on creating the 1st vlan/bridge.

The network setup is:

cloned_interfaces="lagg0"
ifconfig_ix0="up mtu 9000 -lro"
ifconfig_ix1="up mtu 9000 -lro"
ifconfig_lagg0="laggproto lacp laggport ix0 laggport ix1 10.0.10.17/24"
defaultrouter="10.0.10.1"

vm-bhyve creates bridges according to following config:

switch_list="br4 br7 br8"
vlan_br4="4"
ports_br4="lagg0"
vlan_br7="7"
ports_br7="lagg0"
vlan_br8="8"
ports_br8="lagg0"

As soon as vm-bhyve create the first bridge and vlan, the system freezes hard.
Sadly, installing a debug kernel doesn't help; the magic sysrequest key
combination is ignored.

I extracted the network commands executed by vm-bhyve startup script:

ifconfig bridge create
ifconfig bridge0 description something up
ifconfig vlan create
<-- system freezes here -->
ifconfig vlan0 vlandev lagg0 vlan 4 description something up
ifconfig bridge0 addm vlan0

Inserting "sleep 1" after "ifconfig vlan create" seems to fix it. Even minor
delays (e.g. a simple echo to the EFI console after each command) seem to fix
it. Without the delay, changes are about 90% that the system freezes.

This problem seems to occur only with the ixgbe driver. In previous tests with
a NetXtreme II BCM57810 card and the bxe driver everything worked fine, though
the bxe driver seems to lack hardware vlan support which was the reason to
replace it with the Intel card.

It looks like a nasty race condition and I'm not really happy with patching
vm-bhyve, hoping that the (blindly inserted) workaround does the trick. 

The server is a DL380 Gen9. The network cards is an off the shelf Intel 82599ES
(i.e. not a HP branded one).

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