Suspension not possible due to hanging vfs access

[DarkTrick]

Note: The setup I describe here is perhaps a little special, but the problem itself is - I think - a rather general one.

Reproduce
=========
- Setup a vm (locally)
- Setup an smb-server within the vm and create a read/writable folder
- On physical system: Open Visual Studio Code in that folder (`code ./` while in folder or Menu -> File -> OpenFolder)
- < Now VSCode on the host accesses the files on the guest >
- Pause the VM
- Start suspension
- EXPECTED: suspension works
- ACTUAL: suspension fails with syslog below:

Remarks
=======
It seems, that hanging fs-access actions of an application prevent suspension. I had similar problems with Thunar hanging while trying to opening an inaccessible samba share (non-VM that time)

Syslog
=======
myuser kernel: [347533.623866] Freezing of tasks failed after 20.003 seconds (5 tasks refusing to freeze, wq_busy=0):
myuser kernel: [347533.624460] code D 0 266587 266536 0x00004004
myuser kernel: [347533.624472] Call Trace:
myuser kernel: [347533.624495] __schedule+0x212/0x5d0
myuser kernel: [347533.624504] schedule+0x55/0xc0
myuser kernel: [347533.624514] d_alloc_parallel+0x42e/0x4a0
myuser kernel: [347533.624530] ? wake_up_q+0xa0/0xa0
myuser kernel: [347533.624538] __lookup_slow+0x5b/0x150
myuser kernel: [347533.624547] walk_component+0x141/0x1b0
myuser kernel: [347533.624556] link_path_walk.part.0+0x221/0x360
myuser kernel: [347533.624562] ? path_init+0x269/0x410
myuser kernel: [347533.624570] path_lookupat+0x3f/0x1c0
myuser kernel: [347533.624579] filename_lookup+0xaa/0x1b0
myuser kernel: [347533.624595] ? __check_object_size.part.0+0x128/0x150
myuser kernel: [347533.624606] ? __check_object_size+0x1c/0x20
myuser kernel: [347533.624618] ? strncpy_from_user+0x4c/0x150
myuser kernel: [347533.624626] ? getname_flags.part.0+0x4c/0x1b0
myuser kernel: [347533.624635] user_path_at_empty+0x59/0x90
myuser kernel: [347533.624645] vfs_statx+0x81/0x120
myuser kernel: [347533.624655] __do_sys_newstat+0x3e/0x70
myuser kernel: [347533.624666] ? vfs_write+0x169/0x200
myuser kernel: [347533.624677] ? fput+0x13/0x20
myuser kernel: [347533.624691] ? __prepare_exit_to_usermode+0x62/0xe0
myuser kernel: [347533.624702] ? __syscall_return_slowpath+0x31/0x160
myuser kernel: [347533.624710] __x64_sys_newstat+0x16/0x20
myuser kernel: [347533.624718] do_syscall_64+0x49/0xc0
myuser kernel: [347533.624728] entry_SYSCALL_64_after_hwframe+0x44/0xa9
myuser kernel: [347533.624737] RIP: 0033:0x7fc0b518504a
myuser kernel: [347533.624742] RSP: 002b:00007fc0b0b56858 EFLAGS: 00000246 ORIG_RAX: 0000000000000004
myuser kernel: [347533.624751] RAX: ffffffffffffffda RBX: 00002a263d3326e0 RCX: 00007fc0b518504a
myuser kernel: [347533.624755] RDX: 00007fc0b0b569e0 RSI: 00007fc0b0b569e0 RDI: 00002a263d3326e0
myuser kernel: [347533.624760] RBP: 00007fc0b0b58a10 R08: 0000000000000001 R09: aaaaaaaaaaaaaaaa
myuser kernel: [347533.624764] R10: 0000000000000fff R11: 0000000000000246 R12: 0000000000000007
myuser kernel: [347533.624769] R13: 00002a263d66e340 R14: 00007fc0b0b59500 R15: 00002a263d66e2d0
myuser kernel: [347533.624780] code D 0 266588 266536 0x00004004
myuser kernel: [347533.624787] Call Trace:
myuser kernel: [347533.624796] __schedule+0x212/0x5d0
myuser kernel: [347533.624804] schedule+0x55/0xc0
myuser kernel: [347533.624811] d_alloc_parallel+0x42e/0x4a0
myuser kernel: [347533.624823] ? wake_up_q+0xa0/0xa0
myuser kernel: [347533.624831] __lookup_slow+0x5b/0x150
myuser kernel: [347533.624839] walk_component+0x141/0x1b0
myuser kernel: [347533.624847] link_path_walk.part.0+0x221/0x360
myuser kernel: [347533.624853] ? path_init+0x269/0x410
myuser kernel: [347533.624861] path_lookupat+0x3f/0x1c0
myuser kernel: [347533.624869] filename_lookup+0xaa/0x1b0
myuser kernel: [347533.624883] ? __check_object_size.part.0+0x128/0x150
myuser kernel: [347533.624894] ? __check_object_size+0x1c/0x20
myuser kernel: [347533.624904] ? strncpy_from_user+0x4c/0x150
myuser kernel: [347533.624912] ? getname_flags.part.0+0x4c/0x1b0
myuser kernel: [347533.624920] user_path_at_empty+0x59/0x90
myuser kernel: [347533.624930] vfs_statx+0x81/0x120
myuser kernel: [347533.624940] __do_sys_newstat+0x3e/0x70
myuser kernel: [347533.624950] ? vfs_write+0x169/0x200
myuser kernel: [347533.624961] ? fput+0x13/0x20
myuser kernel: [347533.624972] ? __prepare_exit_to_usermode+0x62/0xe0
myuser kernel: [347533.624983] ? __syscall_return_slowpath+0x31/0x160
myuser kernel: [347533.624992] __x64_sys_newstat+0x16/0x20
myuser kernel: [347533.624998] do_syscall_64+0x49/0xc0
myuser kernel: [347533.625008] entry_SYSCALL_64_after_hwframe+0x44/0xa9
myuser kernel: [347533.625013] RIP: 0033:0x7fc0b518504a
myuser kernel: [347533.625017] RSP: 002b:00007fc0b0355858 EFLAGS: 00000246 ORIG_RAX: 0000000000000004
myuser kernel: [347533.625024] RAX: ffffffffffffffda RBX: 00002a263df64000 RCX: 00007fc0b518504a
myuser kernel: [347533.625028] RDX: 00007fc0b03559e0 RSI: 00007fc0b03559e0 RDI: 00002a263df64000
myuser kernel: [347533.625031] RBP: 00007fc0b0357a10 R08: 0000000000000001 R09: aaaaaaaaaaaaaaaa
myuser kernel: [347533.625035] R10: 0000000000000fff R11: 0000000000000246 R12: 0000000000000007
myuser kernel: [347533.625039] R13: 00002a263e02dc40 R14: 00007fc0b0358500 R15: 00002a263e02dbd0
myuser kernel: [347533.625047] code D 0 266589 266536 0x00004004

lsb_release -rd
================
Description: Ubuntu 20.10
Release: 20.10

cat /proc/version_signature
==========================================
Ubuntu 5.8.0-54.61-generic 5.8.18

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: linux-image-5.8.0-54-generic 5.8.0-54.61
ProcVersionSignature: Ubuntu 5.8.0-54.61-generic 5.8.18
Uname: Linux 5.8.0-54-generic x86_64
ApportVersion: 2.20.11-0ubuntu50.7
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: nimono 1384 F.... pulseaudio
 /dev/snd/pcmC0D3p: nimono 1384 F...m pulseaudio
CasperMD5CheckResult: skip
CurrentDesktop: XFCE
Date: Tue Jun 1 16:37:56 2021
MachineType: FUJITSU FMVWB3U27
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.8.0-54-generic root=UUID=fe637d00-125b-4a54-adce-3711830d450b ro acpi_osi=! "acpi_osi=Windows 2015" resume=UUID=bdfdad69-4c0d-4b99-a962-d88c977da8a3
RelatedPackageVersions:
 linux-restricted-modules-5.8.0-54-generic N/A
 linux-backports-modules-5.8.0-54-generic N/A
 linux-firmware 1.190.5
RfKill:
 0: phy0: Wireless LAN
  Soft blocked: no
  Hard blocked: no
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 01/23/2018
dmi.bios.release: 1.7
dmi.bios.vendor: FUJITSU // Insyde Software Corp.
dmi.bios.version: Version 1.07
dmi.board.name: FJNB2BB
dmi.board.vendor: FUJITSU
dmi.board.version: A2
dmi.chassis.type: 10
dmi.chassis.vendor: FUJITSU
dmi.modalias: dmi:bvnFUJITSU//InsydeSoftwareCorp.:bvrVersion1.07:bd01/23/2018:br1.7:svnFUJITSU:pnFMVWB3U27:pvr:rvnFUJITSU:rnFJNB2BB:rvrA2:cvnFUJITSU:ct10:cvr:
dmi.product.family: LIFEBOOK-JR
dmi.product.name: FMVWB3U27
dmi.sys.vendor: FUJITSU

[DarkTrick (darktrick1337)]

Syslog of a case, where virtual machine was not paused - not even touched. I tried to suspend right after opening a youtube tab in firefox.