Using bcache for / leads to hung processes

[Francis Ginther]

I've used maas 1.9.1 to setup a bcache partition mount as /. The bcache is made of a 400GB SSD backed by sda-part2. The sda drive is a 1TB disk with 1GB carved out for /boot (sda-part1) and the rest given to sda-part2. I believe the bcache mode is set to write-through.

Within an hour of this machine being deployed (it's being used as a node in a landscape autopilot openstack deployment) it starts showing hung processes. The output of 'ps faxw' (attached as 'amco-process-list.txt) shows lots of process in the 'D' state and launching more processes that write to the disk will likely get stuck (for example the 'apt-get install python-jenkins' process).

This is reproducible.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-3.13.0-85-generic 3.13.0-85.129
ProcVersionSignature: User Name 3.13.0-85.129-generic 3.13.11-ckt36
Uname: Linux 3.13.0-85-generic x86_64
AlsaDevices:
 total 0
 crw-rw---- 1 root audio 116, 1 May 6 03:07 seq
 crw-rw---- 1 root audio 116, 33 May 6 03:07 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: amd64
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:
Date: Fri May 6 14:24:20 2016
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
MachineType: HP ProLiant DL360e Gen8
PciMultimedia:

ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcFB:

ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.13.0-85-generic root=UUID=cd48c2ff-f38e-4892-a5e2-8862e4412c29 ro console=ttyS0
RelatedPackageVersions:
 linux-restricted-modules-3.13.0-85-generic N/A
 linux-backports-modules-3.13.0-85-generic N/A
 linux-firmware 1.127.22
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 08/02/2014
dmi.bios.vendor: HP
dmi.bios.version: P73
dmi.chassis.type: 23
dmi.chassis.vendor: HP
dmi.modalias: dmi:bvnHP:bvrP73:bd08/02/2014:svnHP:pnProLiantDL360eGen8:pvr:cvnHP:ct23:cvr:
dmi.product.name: ProLiant DL360e Gen8
dmi.sys.vendor: HP

[Brad Figg (brad-figg)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

Did this issue start happening after an update/upgrade? Was there a prior kernel version where you were not having this particular problem?

Would it be possible for you to test the latest upstream kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v4.6 kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.6-rc6-wily/

[Francis Ginther (fginther)]

This problem does go away when using the wily, hwe-w, kernel. I'm unable to test the mainline kernel as requested in the above comment at this time. I will try to come back to it when I have the hw configuration available again.

[Launchpad Janitor (janitor)]

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