tuxonice not working, how to debug?

[beelze]

I'm running 4.5.0-pf4 kernel from pf-sources:

CONFIG_TOI_CORE=y
# CONFIG_TOI_FILE is not set
CONFIG_TOI_SWAP=y
CONFIG_TOI_CRYPTO=y
CONFIG_TOI_USERUI=y
CONFIG_TOI_USERUI_DEFAULT_PATH="/sbin/tuxoniceui"
CONFIG_TOI_DEFAULT_IMAGE_SIZE_LIMIT=-2
# CONFIG_TOI_KEEP_IMAGE is not set
# CONFIG_TOI_REPLACE_SWSUSP is not set
# CONFIG_TOI_IGNORE_LATE_INITCALL is not set
CONFIG_TOI_DEFAULT_WAIT=30
CONFIG_TOI_DEFAULT_EXTRA_PAGES_ALLOWANCE=2000
CONFIG_TOI_CHECKSUM=y
CONFIG_TOI=y
CONFIG_TOI_ZRAM_SUPPORT=y

kernel cmdline includes resume=UUID=031b77a5-03c3-427f-a1c1-a9960846032c

# cat /sys/power/tuxonice/debug_info          
TuxOnIce debugging info:
- TuxOnIce core  : 3.3
- Kernel Version : 4.5.0-pf4-pf-Nov11
- Compiler vers. : 4.9
- Attempt number : 0
- Parameters     : 0 532480 0 0 -2 0
- Overall expected compression percentage: 0.
- Checksum method is 'md4'.
  0 pages resaved in atomic copy.
- Compressor is 'lzo'.
- Block I/O active.
- Max outstanding reads 1. Max writes 1.
  Memory_needed: 1024 x (4096 + 376 + 128) = 4710400 bytes.
  Free mem throttle point reached 0.
- Swap Allocator enabled.
  Swap available for image: 8388606 pages.
- No I/O speed stats available.
- Extra pages    : 0 used/2000.
- Result         : No hibernation attempts so far.

# dmesg | grep -i tuxon                           
[    0.273811] TuxOnIce 3.3 (http://tuxonice.net)
[    0.754267] TuxOnIce: No image found.

/sbin/tuxoniceui -t is working. When I'm echoing to /sys/power/tuxonice/do_hibernate, I see nothing happening except switching displays to text mode, but tuxonice «succeeds»:

kernel: TuxOnIce 3.3, with support for checksumming, usm, comp
ression, block i/o, swap storage, userui.
kernel: Initiating a hibernation cycle.
kernel: Console is 56x180.
kernel: Starting other threads.
kernel: Freezing user space processes ... 
kernel: (elapsed 0.001 seconds) done.
kernel: Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
kernel: Restarting kernel threads ... done.
kernel: Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
kernel: Restarting tasks ... done.
kernel: video LNXVIDEO:00: Restoring backlight state
kernel: TuxOnIce debugging info:\x0a- TuxOnIce core  : 3.3\x0a - Kernel Version : 4.5.0-pf4-pf-Nov11\x0a- Compiler vers. : 4.9\x0a- Attempt number : 2\
x0a- Parameters     : 0 532512 0 0 -2 0\x0a- Overall expected compression percentage: 0.
\x0a- Checksum method is 'md4'.\x0a  0 pages resaved in atomic copy.\x0a- Compressor is 
'lzo'.\x0a- Block I/O active.\x0a  Used 0 pages from swap on /dev/sdb1.\x0a  Used 0 page
s from swap on /dev/sda1.\x0a- Max outstanding reads 1. Max writes 0.\x0a  Memory_needed: 1024 x (4096 + 376 + 128) = 4710400 bytes.\x0a  Free mem throttle point reached 0.\x0a- Swap Allocator enabled.\x0a  Swap available for image: 8388606 pages.\x0a- No I/O speed stats available.\x0a- Extra pages    : 0 used/2000.\x0a- Result         : Succeeded.

how can I debug it?