Comment # 4 on bug 1020030 from Paul Neuwirth

Comment on attachment 711296 [details]
dmesg output

had the same effect here twice.
cannot be related to laptopmode/hibernation (not in use).
it's clearly related to btrfs.
in my case I use btrfs with raid 1:
# btrfs filesystem show /
Label: none  uuid: 3d8fa570-b048-4d41-80e2-690a715d9e09
    Total devices 2 FS bytes used 42.35GiB
    devid    1 size 266.09GiB used 44.03GiB path /dev/sda2
    devid    2 size 266.09GiB used 44.03GiB path /dev/sdb2
# btrfs filesystem usage /
Overall:
    Device size:         532.19GiB
    Device allocated:          88.06GiB
    Device unallocated:         444.12GiB
    Device missing:             0.00B
    Used:              84.75GiB
    Free (estimated):         222.87GiB    (min: 222.87GiB)
    Data ratio:                  2.00
    Metadata ratio:              2.00
    Global reserve:         416.00MiB    (used: 0.00B)

Data,RAID1: Size:42.00GiB, Used:41.19GiB
   /dev/sda2      42.00GiB
   /dev/sdb2      42.00GiB

Metadata,RAID1: Size:2.00GiB, Used:1.19GiB
   /dev/sda2       2.00GiB
   /dev/sdb2       2.00GiB

System,RAID1: Size:32.00MiB, Used:16.00KiB
   /dev/sda2      32.00MiB
   /dev/sdb2      32.00MiB

Unallocated:
   /dev/sda2     222.06GiB
   /dev/sdb2     222.06GiB