This can easily be reproduced on another moonshot node with the same 5.0.0-38 kernel (clean deploy with Disco by MAAS)

And issue exists in the proposed 5.0.0-39 kernel as well.

[  OK  ] Reached target Final Step.
[  OK  ] Started Reboot.
[  OK  ] Reached target Reboot.
         Stopping LVM2 metadata daemon...
[  433.924174] kernel BUG at mm/slub.c:305!
[  433.971224] Internal error: Oops - BUG: 0 [#1] SMP
[  434.028703] Modules linked in: dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua gpio_keys_polled input_polldev mailbox_xgene_slimpro crct10dif_ce xgene_rng uio_pdrv_genirq uio sch_fq_codel ib_iser rdma_cm iw_cm ib_cm iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi ip_tables x_tables autofs4 btrfs zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor xor_neon raid6_pq libcrc32c raid1 raid0 multipath linear mlx4_ib ib_uverbs ib_core mlx4_en mlx4_core devlink gpio_dwapb ahci_xgene gpio_xgene_sb
[  434.598420] Process shutdown (pid: 1, stack limit = 0x00000000024008b6)
[  434.677705] CPU: 5 PID: 1 Comm: shutdown Not tainted 5.0.0-38-generic #41-Ubuntu
[  434.766479] Hardware name: HP ProLiant m400 Server Cartridge (DT)
[  434.839504] pstate: 60400005 (nZCv daif +PAN -UAO)
[  434.896885] pc : __slab_free+0x170/0x3d8
[  434.943928] lr : kfree+0x1b4/0x1c8
[  434.984611] sp : ffff000017c2b950
[  435.024253] x29: ffff000017c2b950 x28: ffff00001173c708 
[  435.087888] x27: 0000000000000010 x26: ffff7e003ea93020 
[  435.151524] x25: 0000000000000002 x24: ffff800faa4c2c00 
[  435.215159] x23: ffff800ff6003800 x22: 0000000000000000 
[  435.278794] x21: 000000008020000f x20: ffff800faa4c2c00 
[  435.342429] x19: ffff7e003ea93000 x18: 000000000000000c 
[  435.406063] x17: 0000000000000000 x16: 0000000000000000 
[  435.469700] x15: ffff000010fb7f30 x14: ffff800fab1ef390 
[  435.533334] x13: ffff800ff50ec760 x12: 0000000000000000 
[  435.596969] x11: ffff800ff50ec6d8 x10: 0000000000000040 
[  435.660605] x9 : ffff800fab1ef398 x8 : 0000000000000001 
[  435.724240] x7 : ffff800faa4c2c00 x6 : 0000000000000001 
[  435.787875] x5 : 0000000000210d00 x4 : 0000000000000001 
[  435.851510] x3 : ffff800faa4c2c00 x2 : 0000000000000000 
[  435.915146] x1 : 0000000040000000 x0 : 0000000000210d00 
[  435.978781] Call trace:
[  436.007993]  __slab_free+0x170/0x3d8
[  436.050763]  kfree+0x1b4/0x1c8
[  436.087281]  cm_remove_one+0x21c/0x2b0 [ib_cm]
[  436.140602]  ib_unregister_device+0x100/0x218 [ib_core]
[  436.203300]  mlx4_ib_remove+0x84/0x1f8 [mlx4_ib]
[  436.258703]  mlx4_remove_device+0xcc/0xf8 [mlx4_core]
[  436.319322]  mlx4_unregister_device+0x84/0x158 [mlx4_core]
[  436.385154]  mlx4_unload_one+0x88/0x2c8 [mlx4_core]
[  436.443684]  mlx4_shutdown+0x70/0x88 [mlx4_core]
[  436.499075]  pci_device_shutdown+0x44/0x88
[  436.548208]  device_shutdown+0x134/0x240
[  436.595153]  kernel_restart_prepare+0x44/0x50
[  436.647415]  kernel_restart+0x20/0x68
[  436.691230]  __se_sys_reboot+0x10c/0x230
[  436.738173]  __arm64_sys_reboot+0x24/0x30
[  436.786161]  el0_svc_common+0xa0/0x168
[  436.831018]  el0_svc_handler+0x38/0x78
[  436.875876]  el0_svc+0x8/0xc
[  436.910304] Code: 8b020303 eb14031f 54fff921 d503201f (d4210000) 
[  436.983435] ---[ end trace 5014d8c4f5e4f10d ]---