Course sanity check with mainline kernels:

4.2 OK
4.3 hangs
4.4 hangs
4.5 hang
4.6 - 4.8 no hang, but dumps message (see below)
4.9 OK

Oct  8 11:04:03 ubuntu kernel: [   31.788232] block nbd0: NBD_DISCONNECT
Oct  8 11:04:03 ubuntu kernel: [   31.788286] block nbd0: shutting down socket
Oct  8 11:04:03 ubuntu kernel: [   31.788290] ------------[ cut here ]------------
Oct  8 11:04:03 ubuntu kernel: [   31.788299] WARNING: CPU: 0 PID: 1807 at /home/kernel/COD/linux/kernel/softirq.c:150 __local_bh_enable_ip+0x6b/0x80
Oct  8 11:04:03 ubuntu kernel: [   31.788301] Modules linked in: squashfs loop fuse nbd nls_iso8859_1 vfat fat snd_hda_codec_generic snd_hda_intel snd_hda_codec ppdev snd_hda_core virtio_console snd_hwdep virtio_balloon snd_pcm joydev input_leds efi_pstore led_class snd_timer efivars serio_raw snd i2c_piix4 soundcore acpi_cpufreq parport_pc 8250_fintek processor parport qemu_fw_cfg mac_hid ib_iser rdma_cm iw_cm ib_cm ib_sa ib_mad ib_core ib_addr configfs iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi efivarfs autofs4 ext4 crc16 jbd2 mbcache btrfs raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor hid_generic usbhid hid raid6_pq libcrc32c crc32c_generic raid1 raid0 multipath linear md_mod ata_generic virtio_net virtio_blk pata_acpi qxl ttm drm_kms_helper syscopyarea crct10dif_pclmul crc32_pclmul sysfillrect sysimgblt crc32c_intel fb_sys_fops ghash_clmulni_intel drm ata_piix intel_agp libata aesni_intel intel_gtt aes_x86_64 lrw gf128mul glue_helper uhci_hcd ablk_helper ehci_pci cryptd ehci_hcd agpgart scsi_mod virtio_pci psmouse usbcore virtio_ring virtio usb_common floppy button
Oct  8 11:04:03 ubuntu kernel: [   31.788400] CPU: 0 PID: 1807 Comm: nbd-client Not tainted 4.6.0-040600-generic #201606100558
Oct  8 11:04:03 ubuntu kernel: [   31.788402] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
Oct  8 11:04:03 ubuntu kernel: [   31.788404]  0000000000000086 0000000047e82912 ffff88039807faa8 ffffffff8135f483
Oct  8 11:04:03 ubuntu kernel: [   31.788409]  0000000000000000 0000000000000000 ffff88039807fae8 ffffffff810814db
Oct  8 11:04:03 ubuntu kernel: [   31.788412]  0000009647e82912 0000000000000200 ffff8803987d8840 ffff880393e74070
Oct  8 11:04:03 ubuntu kernel: [   31.788416] Call Trace:
Oct  8 11:04:03 ubuntu kernel: [   31.788445]  [<ffffffff8135f483>] dump_stack+0x63/0x90
Oct  8 11:04:03 ubuntu kernel: [   31.788448]  [<ffffffff810814db>] __warn+0xcb/0xf0
Oct  8 11:04:03 ubuntu kernel: [   31.788451]  [<ffffffff8108160d>] warn_slowpath_null+0x1d/0x20
Oct  8 11:04:03 ubuntu kernel: [   31.788455]  [<ffffffff81086bfb>] __local_bh_enable_ip+0x6b/0x80
Oct  8 11:04:03 ubuntu kernel: [   31.788461]  [<ffffffff81579217>] lock_sock_nested+0x57/0x70
Oct  8 11:04:03 ubuntu kernel: [   31.788471]  [<ffffffff8160e50b>] inet_shutdown+0x3b/0x110
Oct  8 11:04:03 ubuntu kernel: [   31.788474]  [<ffffffff815738a0>] kernel_sock_shutdown+0x10/0x20
Oct  8 11:04:03 ubuntu kernel: [   31.788481]  [<ffffffffc064ae6a>] sock_shutdown+0x4a/0xa0 [nbd]
Oct  8 11:04:03 ubuntu kernel: [   31.788486]  [<ffffffffc064b4d5>] __nbd_ioctl+0x615/0xb70 [nbd]
Oct  8 11:04:03 ubuntu kernel: [   31.788492]  [<ffffffff810b537a>] ? select_idle_sibling+0x2a/0x120
Oct  8 11:04:03 ubuntu kernel: [   31.788497]  [<ffffffff810b65db>] ? select_task_rq_fair+0x61b/0x730
Oct  8 11:04:03 ubuntu kernel: [   31.788504]  [<ffffffff810ad297>] ? try_to_wake_up+0x47/0x3c0
Oct  8 11:04:03 ubuntu kernel: [   31.788507]  [<ffffffff810ad6b2>] ? default_wake_function+0x12/0x20
Oct  8 11:04:03 ubuntu kernel: [   31.788519]  [<ffffffff812375b3>] ? pollwake+0x73/0x90
Oct  8 11:04:03 ubuntu kernel: [   31.788526]  [<ffffffff810ad6a0>] ? wake_up_q+0x70/0x70
Oct  8 11:04:03 ubuntu kernel: [   31.788532]  [<ffffffff810c5372>] ? __wake_up_common+0x52/0x90
Oct  8 11:04:03 ubuntu kernel: [   31.788541]  [<ffffffff810ee653>] ? current_fs_time+0x23/0x30
Oct  8 11:04:03 ubuntu kernel: [   31.788546]  [<ffffffff812c6168>] ? security_capable+0x48/0x60
Oct  8 11:04:03 ubuntu kernel: [   31.788550]  [<ffffffffc064ba8d>] nbd_ioctl+0x5d/0x7d [nbd]
Oct  8 11:04:03 ubuntu kernel: [   31.788557]  [<ffffffff8133d964>] blkdev_ioctl+0x274/0x920
Oct  8 11:04:03 ubuntu kernel: [   31.788564]  [<ffffffff81221b49>] ? __vfs_write+0xc9/0x120
Oct  8 11:04:03 ubuntu kernel: [   31.788574]  [<ffffffff8125e3ad>] block_ioctl+0x3d/0x50
Oct  8 11:04:03 ubuntu kernel: [   31.788577]  [<ffffffff81236531>] do_vfs_ioctl+0xa1/0x5b0
Oct  8 11:04:03 ubuntu kernel: [   31.788582]  [<ffffffff81222489>] ? vfs_write+0x149/0x1a0
Oct  8 11:04:03 ubuntu kernel: [   31.788585]  [<ffffffff81236ab9>] SyS_ioctl+0x79/0x90
Oct  8 11:04:03 ubuntu kernel: [   31.788601]  [<ffffffff816a09b6>] entry_SYSCALL_64_fastpath+0x1e/0xa8
Oct  8 11:04:03 ubuntu kernel: [   31.788605] ---[ end trace 017ff4e61fb69ab3 ]---
Oct  8 11:04:03 ubuntu kernel: [   31.788687] block nbd0: Receive control failed (result -32)
Oct  8 11:04:05 ubuntu kernel: [   33.299189] nbd: unregistered device at major 43