xen domU lost networking after upgrading to stable-4.13

[Tomas Mozes <hydrapolic@xxxxxxxxx>]

Hello,
I was trying to upgrade one of my Xen dom0 from stable-4.12 to stable-4.13. The machine has been rock stable on 4.12, but after the upgrade and reboot, one of the xen-domU (there are 15 virtual machines on the host) lost it's networking with this in the kernel log:

[ 1226.477594] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[ 1226.477607] rcu:     0-....: (8 GPs behind) idle=b82/0/0x1 softirq=55602/55602 fqs=5250
[ 1226.477613]  (detected by 8, t=21002 jiffies, g=151513, q=854)
[ 1226.477619] Sending NMI from CPU 8 to CPUs 0:
[ 1226.478642] NMI backtrace for cpu 0
[ 1226.478646] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.55-gentoo #1
[ 1226.478648] Hardware name: Xen HVM domU, BIOS 4.13.1 08/03/2020
[ 1226.478650] RIP: 0010:io_serial_out+0x11/0x20
[ 1226.478654] Code: 8b 57 08 d3 e6 01 f2 ec 0f b6 c0 c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 0f b6 8f b9 00 00 00 89 d0 8b 57 08 d3 e6 01 f2 ee <c3> 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 0f b6 87 ba 00 00 00
[ 1226.478656] RSP: 0018:ffffc90000003e20 EFLAGS: 00000002
[ 1226.478659] RAX: 0000000000000074 RBX: ffff888271e1c000 RCX: 0000000000000000
[ 1226.478661] RDX: 00000000000003f8 RSI: 0000000000000000 RDI: ffffffff832fcc00
[ 1226.478663] RBP: ffffffff832fcc00 R08: 00000000000000b0 R09: ffff888274051188
[ 1226.478665] R10: 0000000000000000 R11: ffffffff82a5dde8 R12: 000000000000000a
[ 1226.478667] R13: 0000000000000020 R14: 0000000000000001 R15: ffff888273c07034
[ 1226.478669] FS:  0000000000000000(0000) GS:ffff888276200000(0000) knlGS:0000000000000000
[ 1226.478671] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1226.478673] CR2: 00007f3bbc06d158 CR3: 000000026427e003 CR4: 00000000001606f0
[ 1226.478674] Call Trace:
[ 1226.478674]  <IRQ>
[ 1226.478675]  serial8250_tx_chars+0xdb/0x220
[ 1226.478677]  serial8250_handle_irq.part.0+0xc5/0x100
[ 1226.478678]  serial8250_default_handle_irq+0x36/0x60
[ 1226.478679]  serial8250_interrupt+0x51/0xa0
[ 1226.478682]  __handle_irq_event_percpu+0x3d/0x180
[ 1226.478683]  handle_irq_event_percpu+0x2c/0x80
[ 1226.478685]  handle_irq_event+0x31/0x4e
[ 1226.478688]  handle_edge_irq+0x7e/0x190
[ 1226.478688]  generic_handle_irq+0x1f/0x30
[ 1226.478708]  __evtchn_fifo_handle_events+0x143/0x190
[ 1226.478709]  __xen_evtchn_do_upcall+0x53/0x90
[ 1226.478710]  xen_evtchn_do_upcall+0x22/0x40
[ 1226.478711]  xen_hvm_callback_vector+0xf/0x20
[ 1226.478712]  </IRQ>
[ 1226.478713] RIP: 0010:native_safe_halt+0xe/0x10
[ 1226.478715] Code: 8b 00 a8 08 74 80 eb c2 90 90 90 90 e9 07 00 00 00 0f 00 2d 34 a8 4e 00 f4 c3 66 90 e9 07 00 00 00 0f 00 2d 24 a8 4e 00 fb f4 <c3> 90 41 54 55 53 e8 17 24 47 ff 65 8b 2d 60 37 2e 7e 0f 1f 44 00
[ 1226.478716] RSP: 0018:ffffffff82a03e98 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff0c
[ 1226.478719] RAX: ffffffff81d2c820 RBX: 0000000000000000 RCX: 0000000000000001
[ 1226.478720] RDX: 0000000000105b7e RSI: 7ffffee81a200469 RDI: 0000000000000082
[ 1226.478722] RBP: 0000000000000000 R08: 000000cd42e4dffb R09: 0000011875f079d6
[ 1226.478723] R10: 0000000000000000 R11: 0000000000012000 R12: ffffffff82a15780
[ 1226.478726] R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff82a15780
[ 1226.478727]  ? __sched_text_end+0x6/0x6
[ 1226.478728]  default_idle+0x15/0x130
[ 1226.478730]  do_idle+0x1e8/0x250
[ 1226.478732]  cpu_startup_entry+0x14/0x20
[ 1226.478733]  start_kernel+0x4c8/0x4ea
[ 1226.478735]  secondary_startup_64+0xa4/0xb0

Xen dom0 config:
GRUB_CMDLINE_XEN="dom0_mem=4G gnttab_max_frames=256 ucode=scan loglvl=all guest_loglvl=all console_to_ring console_timestamps=date conring_size=1m smt=true sched=credit"

Xen domU config:
name = "test"
kernel = "kernel-5.4.55-gentoo-xen"
memory = 10000
vcpus = 12
vif = [ '' ]
disk = [
'/dev/vg_data/test_root,raw,xvda,rw',
]
extra = "root=/dev/xvda net.ifnames=0 console=ttyS0 console=ttyS0,38400n8"
type = "hvm"
sdl = 0
vnc = 0
serial='pty'
xen_platform_pci=1
max_grant_frames = 256

Any tips appreciated, thanks,
Tomas