Problem shutting down with bcache+LUKS+btrfs

Question

Hello all! I've a little problem that I hope someone can help me with.
A have a fresh Arch Install fully upgraded on a Dell Inpiron 15R SE 7520. In this setup, my root partition uses bcache (from kernel 3.10.3-1, not from the AUR package) for SSD caching. On top of bcache I use LUKS and finally on top of all that, btfs.
The setup boots, runs and works, but there is a problem: it won't shutdown.
When I try to shutdown with "halt" or "shutdown -h now" I get:
Detaching DM devices.
Detaching DM 253:0.
Could not detach DM /dev/dm-0: Device or resource busy
Cannot finalize remaining file systems and devices, giving up.
[ 1309.417073] mei_me 0000:00:16.0: stop
[ 1341.773926] ata3.00: exception Emask 0x0 SErr 0x0 action 0x6 frozen
[ 1341.773978] ata3.00: cmd a0/00:00:00:08:00/00:00:00:00:00/a0 tag 0 pio 16392 in
[ 1341.773978]              res 40/00:03:00:00:00/00:00:00:00:00/a0 Emask 0x4 (timeout)
[ 1341.774038] ata3.00: status: { DRDY }
[ 1341.811061] ata3: COMRESET failed (errno=-16)
[ 1341.848244] ata3: COMRESET failed (errno=-16)
[ 1341.924857] ata3: COMRESET failed (errno=-16)
[ 1341.943453] ata3: COMRESET failed (errno=-16)
[ 1341.943498] ata3: reset failed, giving up
After that it just stays there, complaining from time to time that "poweroff:857" is blocked for more than 120 seconds and never shutdown if i don't hold the power button.
I'm using the shutdown hook on mkinitcpio. To debug the issue I put "/bin/ash" on /run/initramfs/shutdown and dropped into a shell. In the shell I can't "umount" or "crypsetup luksClose" the root partition, all of them accusing "Device or resource busy", even though lsof says there is nothing using it.
It does not appear to cause any form of file system corruption. I noticed that btrfs identifies the partition as a ssd and automatically mounts with that option, even tough only the cache is ssd. I thought maybe that is the problem, but couldn't find an option to disable btrfs from doing this automagically.
Any help is appreciated.

Answer 1

Bolche wrote:all of them accusing "Device or resource busy", even though lsof says there is nothing using it.
Might be a kernel bug. Perhaps dirty pages on the cache device prevent the backing device from being unmounted.
Bolche wrote:I noticed that btrfs identifies the partition as a ssd and automatically mounts with that option, even tough only the cache is ssd. I thought maybe that is the problem, but couldn't find an option to disable btrfs from doing this automagically.
You should be able to invert the option by passing 'nossd', but this definitely shouldn't be related to the problem.