Unable to mount a btrfs filesystem smaller than 320M on Xenial P8

[Po-Hsu Lin]

This issue will happen to a btrfs filesystem <= 320M, and this was not spotted on any other architecture / kernel. Only this one, X-4.4 and T-4.4

# TMPIMG0=/tmp/test0.img
# DEV0=`losetup -f`
# truncate --size 256M $TMPIMG0
# losetup $DEV0 $TMPIMG0
# mkfs.btrfs -f $DEV0
btrfs-progs v4.4
See http://btrfs.wiki.kernel.org for more information.

Performing full device TRIM (256.00MiB) ...
Label: (null)
UUID: ca007094-ddd4-42e9-bd6d-78c6de03dc66
Node size: 65536
Sector size: 65536
Filesystem size: 256.00MiB
Block group profiles:
  Data: single 8.00MiB
  Metadata: DUP 40.00MiB
  System: DUP 12.00MiB
SSD detected: no
Incompat features: extref, skinny-metadata
Number of devices: 1
Devices:
   ID SIZE PATH
    1 256.00MiB /dev/loop1

# mount $DEV0 $MNT
mount: mount /dev/loop1 on /tmp/mnt failed: No space left on device

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.4.0-141-generic 4.4.0-141.167
ProcVersionSignature: Ubuntu 4.4.0-141.167-generic 4.4.162
Uname: Linux 4.4.0-141-generic ppc64le
AlsaDevices:
 total 0
 crw-rw---- 1 root audio 116, 1 Jan 30 03:23 seq
 crw-rw---- 1 root audio 116, 33 Jan 30 03:23 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: ppc64el
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
Date: Wed Jan 30 03:35:17 2019
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
Lsusb:
 Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
 Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
PciMultimedia:

ProcFB:

ProcKernelCmdLine: root=/dev/mapper/mpath0-part2 ro console=hvc0
ProcLoadAvg: 0.00 0.05 0.09 1/1339 5297
ProcSwaps:
 Filename Type Size Used Priority
 /swap.img file 8388544 0 -1
ProcVersion: Linux version 4.4.0-141-generic (buildd@bos02-ppc64el-009) (gcc version 5.4.0 20160609 (Ubuntu/IBM 5.4.0-6ubuntu1~16.04.10) ) #167-Ubuntu SMP Wed Dec 5 10:33:00 UTC 2018
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-141-generic N/A
 linux-backports-modules-4.4.0-141-generic N/A
 linux-firmware 1.157.21
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
cpu_cores: Number of cores present = 20
cpu_coreson: Number of cores online = 20
cpu_dscr: DSCR is 0
cpu_freq:
 min: 3.694 GHz (cpu 159)
 max: 3.694 GHz (cpu 1)
 avg: 3.694 GHz
cpu_runmode:
 Could not retrieve current diagnostics mode,
 No kernel interface to firmware
cpu_smt: SMT=8

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This change was made by a bot.

[Po-Hsu Lin (cypressyew)]

dmesg output for "mkfs.btrfs -f $DEV0"

Jan 30 07:34:39 modoc kernel: [15133.052549] BTRFS: device fsid 835cd012-615c-4486-ae87-c32e13eaf564 devid 1 transid 3 /dev/loop0

dmesg output for "mount $DEV0 $MNT"
Jan 30 07:35:41 modoc kernel: [15195.038642] BTRFS info (device loop0): disk space caching is enabled
Jan 30 07:35:41 modoc kernel: [15195.038649] BTRFS: has skinny extents
Jan 30 07:35:41 modoc kernel: [15195.042148] BTRFS: creating UUID tree
Jan 30 07:35:41 modoc kernel: [15195.138720] BTRFS: failed to create the UUID tree -28
Jan 30 07:35:41 modoc kernel: [15195.246320] BTRFS: open_ctree failed