Comment 0 for bug 1377130

Hi,

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

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