While I have not found out where exactly things go wrong, I could confirm that this is related to ppc64el builds using a 64k page size. I build a test kernel with 4k page size and installed it inside the VM. With that bcache-super-show will will reflect the correct status after activation and also the superblock magic will remain intact when breaking the cache and backing device.
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1602299 Title: bcache is unstable on ppc64el Status in linux package in Ubuntu: Confirmed Bug description: Stopping and unregistering bcache caches and backing devices results in losing the bcache superblock on devices rendering bcached devices corrupt or broken. 1. Ubuntu 4.4.0-28.47-generic 4.4.13 2. attaching lspci log 3. Description: Ubuntu 16.04 LTS Release: 16.04 4. # apt-cache policy linux-image linux-image: Installed: (none) Candidate: (none) Version table: root@rharper-vm1:~# apt-cache policy linux-image-generic linux-image-generic: Installed: (none) Candidate: 4.4.0.28.30 Version table: 4.4.0.28.30 500 500 http://ports.ubuntu.com/ubuntu-ports xenial-updates/main ppc64el Packages 500 http://ports.ubuntu.com/ubuntu-ports xenial-security/main ppc64el Packages 4.4.0.21.22 500 500 http://ports.ubuntu.com/ubuntu-ports xenial/main ppc64el Packages 5. After creating bcache devices, upon reboot they continue to remain as bcache devices for use 6. Sometimes after reboot either the cache device, or the backing device loses the bcache-super-block rendering them useless to the bcache module (it fails to detect them). ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: linux-image-4.4.0-28-generic 4.4.0-28.47 ProcVersionSignature: Ubuntu 4.4.0-28.47-generic 4.4.13 Uname: Linux 4.4.0-28-generic ppc64le AlsaDevices: total 0 crw-rw---- 1 root audio 116, 1 Jul 11 21:30 seq crw-rw---- 1 root audio 116, 33 Jul 11 21:30 timer AplayDevices: Error: [Errno 2] No such file or directory: 'aplay' ApportVersion: 2.20.1-0ubuntu2.1 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: CRDA: N/A Date: Tue Jul 12 14:20:24 2016 IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig' Lsusb: Bus 001 Device 003: ID 0627:0001 Adomax Technology Co., Ltd Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub PciMultimedia: ProcEnviron: TERM=screen PATH=(custom, no user) LANG=en_US.UTF-8 SHELL=/bin/bash ProcFB: 0 OFfb vga ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinux-4.4.0-28-generic root=LABEL=cloudimg-rootfs earlyprintk ProcLoadAvg: 6.28 4.78 4.12 1/133 4838 ProcLocks: 1: POSIX ADVISORY WRITE 1306 00:11:541 0 EOF 2: FLOCK ADVISORY WRITE 918 00:11:521 0 EOF 3: POSIX ADVISORY WRITE 875 00:11:507 0 EOF 4: POSIX ADVISORY WRITE 870 00:11:123 0 EOF 5: POSIX ADVISORY WRITE 682 00:11:358 0 EOF ProcSwaps: Filename Type Size Used Priority ProcVersion: Linux version 4.4.0-28-generic (buildd@bos01-ppc64el-018) (gcc version 5.3.1 20160413 (Ubuntu/IBM 5.3.1-14ubuntu2.1) ) #47-Ubuntu SMP Fri Jun 24 10:09:20 UTC 2016 RelatedPackageVersions: linux-restricted-modules-4.4.0-28-generic N/A linux-backports-modules-4.4.0-28-generic N/A linux-firmware N/A 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 = 1 cpu_coreson: Number of cores online = 1 cpu_dscr: DSCR is 0 cpu_freq: min: 3.684 GHz (cpu 0) max: 3.684 GHz (cpu 0) avg: 3.684 GHz cpu_runmode: run-mode=0 cpu_smt: Error: command ['ppc64_cpu', '--smt'] failed with exit code 255: Machine is not SMT capable To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1602299/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
