[Impact]
* Users can get a Warning or even Oops the kernel if
bcache/writeback_percent is set before attaching a
caching device to the bcache device.
* The fix is trivial, upstream, and consists of just
checking whether the caching device is attached in
order to set flags and schedule thread (which oops).
[Test Case]
* See attachment 'setup-bcache-wb_percent-before-attach.sh'
used in comment #5 and #6 to reproduce the problem(s).
* for 'Warning':
# make-bcache -B <BACKING DEVICE>
# make-bcache -C <CACHE DEVICE>
# echo 11 > /sys/block/<BACKING DEVICE>/bcache/writeback_percent
# sleep 1
# echo <CSET_UUID> > /sys/block/<BACKING DEVICE>/bcache/attach
* for 'Oops':
(steps above, but don't run last command / 'attach').
[Regression Potential]
* Low. The fix is trivial, contained, and exclusive to bcache sysfs handler.
* The modified path has been exercised with synthetic testing (script).
[Original Bug Description]
See attached dmesg, each time this server is rebooted it emits a concerning bcache warning.
ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.15.0-54-generic 4.15.0-54.58
ProcVersionSignature: Ubuntu 4.15.0-54.58-generic 4.15.18
Uname: Linux 4.15.0-54-generic x86_64
AlsaVersion: Advanced Linux Sound Architecture Driver Version k4.15.0-54-generic.
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay': 'aplay'
ApportVersion: 2.20.9-0ubuntu7.7
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord': 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/by-path', '/dev/snd/hwC0D2', '/dev/snd/pcmC0D2c', '/dev/snd/pcmC0D3c', '/dev/snd/pcmC0D3p', '/dev/snd/pcmC0D0c', '/dev/snd/pcmC0D0p', '/dev/snd/controlC0', '/dev/snd/hwC1D0', '/dev/snd/pcmC1D3p', '/dev/snd/controlC1', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
Card0.Amixer.info: Error: [Errno 2] No such file or directory: 'amixer': 'amixer'
Card0.Amixer.values: Error: [Errno 2] No such file or directory: 'amixer': 'amixer'
Card1.Amixer.info: Error: [Errno 2] No such file or directory: 'amixer': 'amixer'
Card1.Amixer.values: Error: [Errno 2] No such file or directory: 'amixer': 'amixer'
Date: Wed Jul 24 12:28:06 2019
InstallationDate: Installed on 2013-10-04 (2119 days ago)
InstallationMedia: Ubuntu-Server 13.10 "Saucy Salamander" - Beta amd64 (20130925.1)
MachineType: Supermicro X9DAi
ProcEnviron:
TERM=xterm-256color
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
ProcFB: 0 EFI VGA
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.15.0-54-generic root=UUID=8577302d-1f37-40a6-afcd-385beb26059f ro nomodeset elevator=deadline nvme_core.default_ps_max_latency_us=0 nopti noibrs noibpb
RelatedPackageVersions:
linux-restricted-modules-4.15.0-54-generic N/A
linux-backports-modules-4.15.0-54-generic N/A
linux-firmware 1.173.9
RfKill: Error: [Errno 2] No such file or directory: 'rfkill': 'rfkill'
SourcePackage: linux
UpgradeStatus: Upgraded to bionic on 2018-06-09 (409 days ago)
dmi.bios.date: 05/09/2015
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 3.2
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: X9DAi
dmi.board.vendor: Supermicro
dmi.board.version: 0123456789
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: Supermicro
dmi.chassis.version: 0123456789
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr3.2:bd05/09/2015:svnSupermicro:pnX9DAi:pvr0123456789:rvnSupermicro:rnX9DAi:rvr0123456789:cvnSupermicro:ct3:cvr0123456789:
dmi.product.family: To be filled by O.E.M.
dmi.product.name: X9DAi
dmi.product.version: 0123456789
dmi.sys.vendor: Supermicro
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