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[Launchpad Bug Tracker <1377130@xxxxxxxxxxxxxxxxxx>]

[Expired for linux (Ubuntu) because there has been no activity for 60
days.]

** Changed in: linux (Ubuntu)
       Status: Incomplete => Expired

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

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

Status in bcache-tools package in Ubuntu:
  Invalid
Status in linux package in Ubuntu:
  Expired

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 --writeback --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,but to re-use all disks, you'll need a reboot (cf bug 1377142):
    [  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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