Kernel OOPS on one of the mcdivitts:

| [544599.231964] block nbd0: Attempted send on closed socket
| [544599.231968] block nbd0: Attempted send on closed socket
| [544599.231972] block nbd0: Attempted send on closed socket
| [544599.231975] block nbd0: Attempted send on closed socket
| [544627.046717] INFO: rcu_sched self-detected stall on CPU { 3}  (t=15040176 jiffies g=8751031 c=8751030 q=246988591)
| [544627.046719] Task dump for CPU 3:
| [544627.046723] qemu-nbd        R  running task        0 32375      1 0x0000000a
| [544627.046724] Call trace:
| [544627.046733] [<ffffffc00008acf4>] dump_backtrace+0x0/0x170
| [544627.046737] [<ffffffc00008ae84>] show_stack+0x20/0x2c
| [544627.046740] [<ffffffc0000e066c>] sched_show_task+0xa0/0xf8
| [544627.046742] [<ffffffc0000e3c24>] dump_cpu_task+0x44/0x54
| [544627.046745] [<ffffffc00010bb90>] rcu_dump_cpu_stacks+0x98/0xec
| [544627.046747] [<ffffffc00010f350>] rcu_check_callbacks+0x410/0x740
| [544627.046751] [<ffffffc000114974>] update_process_times+0x40/0x74
| [544627.046754] [<ffffffc0001246d8>] tick_sched_handle.isra.15+0x38/0x7c
| [544627.046756] [<ffffffc000124764>] tick_sched_timer+0x48/0x84
| [544627.046758] [<ffffffc000114ff4>] __run_hrtimer+0x90/0x1d0
| [544627.046760] [<ffffffc000115ae4>] hrtimer_interrupt+0xec/0x28c
| [544627.046764] [<ffffffc00063f4b4>] arch_timer_handler_phys+0x38/0x48
| [544627.046766] [<ffffffc000105554>] handle_percpu_devid_irq+0x90/0x12c
| [544627.046769] [<ffffffc0001010c0>] generic_handle_irq+0x38/0x54
| [544627.046770] [<ffffffc000101404>] __handle_domain_irq+0x64/0xc0
| [544627.046772] [<ffffffc000082478>] gic_handle_irq+0x38/0x88
| [544627.046773] Exception stack(0xffffffc634947610 to 0xffffffc634947730)
| [544627.046776] 7600:                                     00c1a000 ffffffc0 00c1f000 ffffffc0
| [544627.046778] 7620: 34947750 ffffffc6 000ffe0c ffffffc0 00000900 00000000 000001c0 00000000
| [544627.046780] 7640: 00000005 00000000 004a1870 ffffffc0 004a1870 ffffffc0 004a433c ffffffc0
| [544627.046782] 7660: 000000ff 00000000 00b5c658 ffffffc0 6465736f 636f7320 00ba157e 00000000
| [544627.046784] 7680: 00ba1449 00000000 00000000 00000000 00000006 00000000 66666666 20666366
| [544627.046786] 76a0: 34393433 30353737 ec9de100 0038d0cb 0023ceec ffffffc0 004bc7f8 00000000
| [544627.046788] 76c0: aff5f5d0 0000007f 00c1a000 ffffffc0 00c1f000 ffffffc0 00000140 00000000
| [544627.046790] 76e0: 00c1adc0 ffffffc0 00b7c198 ffffffc0 00000001 00000000 00c1f1c0 ffffffc0
| [544627.046792] 7700: 00000003 00000000 00000000 00000000 fff47938 ffffffcf 34947750 ffffffc6
| [544627.046793] 7720: 000ffe08 ffffffc0 34947750 ffffffc6
| [544627.046795] [<ffffffc000085da4>] el1_irq+0x64/0xc0
| [544627.046798] [<ffffffc000100170>] vprintk_emit+0x33c/0x59c
| [544627.046801] [<ffffffc0004c1c4c>] dev_vprintk_emit+0xc8/0x204
| [544627.046802] [<ffffffc0004c1dfc>] dev_printk_emit+0x74/0x84
| [544627.046804] [<ffffffc0004c1e60>] __dev_printk+0x54/0x9c
| [544627.046805] [<ffffffc0004c2114>] dev_err+0x70/0x80
| [544627.046814] [<ffffffbffc3c8544>] __nbd_ioctl+0x810/0x944 [nbd]
| [544627.046817] [<ffffffbffc3c86f4>] nbd_ioctl+0x7c/0x228 [nbd]
| [544627.046821] [<ffffffc0003b2fe8>] blkdev_ioctl+0x1f4/0x770
| [544627.046825] [<ffffffc000245108>] block_ioctl+0x50/0x64
| [544627.046829] [<ffffffc00021e094>] do_vfs_ioctl+0x330/0x5d4
| [544627.046831] [<ffffffc00021e3c4>] SyS_ioctl+0x8c/0xa4