This bug is missing log files that will aid in diagnosing the problem.
>From a terminal window please run:

apport-collect 1377130

and then change the status of the bug to 'Confirmed'.

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to run this command, please add a comment stating that fact and change
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This change has been made by an automated script, maintained by the
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** Changed in: linux (Ubuntu)
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1377130

Title:
  Crash at creation of bcache if caching size > backing size

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  Hi,

  I found a bug that crashes the machine if you create a bcache where
  the caching device size is bigger than backing device.

  This case may happen if you create a bcache with a plan to add a
  bigger disk/partition/raid later to it.

  To reproduce it follow this steps:

  start a vm with utopic-amd64-desktop iso, it must have 2 disks, one of
  16G and on of 8G

  apt-get update && apt-get install bcache-tools
  /dev/sda is 16G caching device
  /dev/sdb is 8G backing device

  make-bcache --write-back --discard -C /dev/sda -B /dev/sdb
  now the machine is hanged.

  if you reboot and reinstall bcache-tools
  the bcache device has been created

  ************************************
  bcache-super-show -f /dev/sda:
  ==============================
  sb.magic              ok
  sb.first_sector               8 [match]
  sb.csum                       45C96B38A79275A7 [match]
  sb.version            0 [cache device]

  dev.label             (empty)
  dev.uuid              155ab65e-e74a-4ca8-91da-467ef696db63
  dev.sectors_per_block 1
  dev.sectors_per_bucket        1024
  dev.cache.first_sector        1024
  dev.cache.cache_sectors       33553408
  dev.cache.total_sectors       33554432
  dev.cache.ordered     no
  dev.cache.discard     yes
  dev.cache.pos         0
  dev.cache.replacement 0 [lru]

  cset.uuid               bcaa2595-bbc8-43a7-8c44-5d0aca0f3fc8

  *****************************************************
  bcache-super-show /dev/sdb:
  =============================================
  sb.magic              ok
  sb.first_sector               8 [match]
  sb.csum                       F37A1BB08A7F5DE7 [match]
  sb.version            1 [backing device]

  dev.label             (empty)
  dev.uuid              341f1c83-1797-4157-aa9e-524107db5606
  dev.sectors_per_block 1
  dev.sectors_per_bucket        1024
  dev.data.first_sector 16
  dev.data.cache_mode   1 [writeback]
  dev.data.cache_state  0 [detached]

  cset.uuid             bcaa2595-bbc8-43a7-8c44-5d0aca0f3fc8
  *****************************************************

  you can format it:
  mkfs.ext4 /dev/bcache0
  Rejet des blocs de périphérique : complété
  Creating filesystem with 2097150 4k blocks and 524288 inodes
  Filesystem UUID: b99a09de-3a92-4a44-82cd-29f75f8bf0c9
  Superblocs de secours stockés sur les blocs :
   32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632

  Allocation des tables de groupe : complété
  Écriture des tables d'i-noeuds : complété
  Création du journal (32768 blocs) : complété
  Écriture des superblocs et de l'information de comptabilité du système de
  fichiers :

  restarting the format gave me an other bug (X.org crashing):
  free from cli:
               total       used       free     shared    buffers     cached
  Mem:       1017168     814040     203128     195568      91264     513064
  -/+ buffers/cache:     209712     807456
  Swap:            0          0          0

  tail /var/log/syslog:
  [  568.016481] [ 4983]     0  4983     3332      121      11        0         
    0 mdadm
  [  568.016483] [ 5259]     0  5259     6703      300      19        0         
    0 mkfs.ext4
  [  568.016484] Out of memory: Kill process 1947 (Xorg) score 38 or sacrifice 
child
  [  568.016485] Killed process 1947 (Xorg) total-vm:313160kB, 
anon-rss:35976kB, file-rss:4232kB
  [  568.707107] systemd-logind[1396]: Failed to start unit user@112.service: 
Unknown unit: user@112.service
  [  568.707113] systemd-logind[1396]: Failed to start user service: Unknown 
unit: user@112.service
  [  568.709876] systemd-logind[1396]: New session c8 of user lightdm.
  [  568.709890] systemd-logind[1396]: Linked /tmp/.X11-unix/X0 to 
/run/user/112/X11-display.

  You can unregister the bcache device:
  [  830.811150] bcache: cached_dev_detach_finish() Caching disabled for sdb
  [  830.949898] bcache: cache_set_free() Cache set 
bcaa2595-bbc8-43a7-8c44-5d0aca0f3fc8 unregistered

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