I/O Error Test 5
================
commit "bcache: stop bcache device when backing device is offline"
Problem: bcache is unaware that a backing device goes offline,
and accepts writes.
Original kernel: bcache doesn't realize backing device is offline.
Modified kernel: bcache device is removed after backing device is offline.
Original
--------
# uname -rv
4.15.0-55-generic #60-Ubuntu SMP Tue Jul 2 18:22:20 UTC 2019
# apt install -y linux-modules-extra-$(uname -r)=4.15.0-55.60
# modprobe scsi_debug dev_size_mb=1024
# dmesg | tail
[ 17.339336] scsi host2: scsi_debug: version 1.86 [20160430]
dev_size_mb=1024, opts=0x0, submit_queues=1, statistics=0
[ 17.339667] scsi 2:0:0:0: Direct-Access Linux scsi_debug 0186
PQ: 0 ANSI: 7
[ 17.339989] sd 2:0:0:0: Power-on or device reset occurred
[ 17.340184] sd 2:0:0:0: Attached scsi generic sg0 type 0
[ 17.348436] sd 2:0:0:0: [sda] 2097152 512-byte logical blocks: (1.07 GB/1.00
GiB)
[ 17.352496] sd 2:0:0:0: [sda] Write Protect is off
[ 17.352501] sd 2:0:0:0: [sda] Mode Sense: 73 00 10 08
[ 17.360686] sd 2:0:0:0: [sda] Write cache: enabled, read cache: enabled,
supports DPO and FUA
[ 17.451956] sd 2:0:0:0: [sda] Attached SCSI disk
# ./setup-sda.sh >/dev/null 2>&1
[ 37.515474] bcache: run_cache_set() invalidating existing data
[ 37.527275] bcache: register_cache() registered cache device dm-0
[ 37.625160] bcache: register_bdev() registered backing device sda
[ 38.466997] bcache: bch_cached_dev_attach() Caching sda as bcache0 on set
0e23e266-6032-4700-a4c9-464964ed1349
# lsblk -e 252
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 1G 0 loop
└─fake-loop0 253:0 0 1024M 0 dm
└─bcache0 251:0 0 1024M 0 disk
sda 8:0 0 1G 0 disk
└─bcache0 251:0 0 1024M 0 disk
# echo writeback > /sys/block/sda/bcache/cache_mode
# echo 1 > /sys/block/sda/device/delete
[ 77.878624] sd 2:0:0:0: [sda] Synchronizing SCSI cache
# sleep 10
#
# dd if=/dev/zero of=/dev/bcache0 bs=4k
[ 120.268072] Buffer I/O error on dev bcache0, logical block 0, lost async
page write
[ 120.271978] Buffer I/O error on dev bcache0, logical block 1, lost async
page write
[ 120.274554] Buffer I/O error on dev bcache0, logical block 2, lost async
page write
[ 120.276671] Buffer I/O error on dev bcache0, logical block 3, lost async
page write
[ 120.278760] Buffer I/O error on dev bcache0, logical block 4, lost async
page write
[ 120.288042] Buffer I/O error on dev bcache0, logical block 5, lost async
page write
[ 120.290178] Buffer I/O error on dev bcache0, logical block 6, lost async
page write
[ 120.296043] Buffer I/O error on dev bcache0, logical block 7, lost async
page write
[ 120.298167] Buffer I/O error on dev bcache0, logical block 8, lost async
page write
[ 120.300220] Buffer I/O error on dev bcache0, logical block 3260, lost async
page write
dd: error writing '/dev/bcache0': No space left on device
262143+0 records in
262142+0 records out
1073733632 bytes (1.1 GB, 1.0 GiB) copied, 3.49705 s, 307 MB/s
# lsblk -e 252
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 1G 0 loop
└─fake-loop0 253:0 0 1024M 0 dm
└─bcache0 251:0 0 1024M 0 disk
Modified
--------
# uname -rv
4.15.0-55-generic #60+test20190703build1bcache1-Ubuntu SMP Wed Jul 3 21:41:37
UTC
# modprobe scsi_debug dev_size_mb=1024
# dmesg | tail
[ 27.855163] scsi host2: scsi_debug: version 1.86 [20160430]
dev_size_mb=1024, opts=0x0, submit_queues=1, statistics=0
[ 27.855497] scsi 2:0:0:0: Direct-Access Linux scsi_debug 0186
PQ: 0 ANSI: 7
[ 27.855829] sd 2:0:0:0: Power-on or device reset occurred
[ 27.855883] sd 2:0:0:0: Attached scsi generic sg0 type 0
[ 27.863979] sd 2:0:0:0: [sda] 2097152 512-byte logical blocks: (1.07 GB/1.00
GiB)
[ 27.868028] sd 2:0:0:0: [sda] Write Protect is off
[ 27.868031] sd 2:0:0:0: [sda] Mode Sense: 73 00 10 08
[ 27.876114] sd 2:0:0:0: [sda] Write cache: enabled, read cache: enabled,
supports DPO and FUA
[ 27.966877] sd 2:0:0:0: [sda] Attached SCSI disk
#
# ./setup-sda.sh >/dev/null 2>&1
[ 46.294586] bcache: run_cache_set() invalidating existing data
[ 46.306769] bcache: register_cache() registered cache device dm-0
[ 46.400510] bcache: register_bdev() registered backing device sda
[ 47.247662] bcache: bch_cached_dev_attach() Caching sda as bcache0 on set
d3d7816b-6bd9-4dea-bf0c-4bde76b45f91
# lsblk -e 252
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 1G 0 loop
└─fake-loop0 253:0 0 1024M 0 dm
└─bcache0 251:0 0 1024M 0 disk
sda 8:0 0 1G 0 disk
└─bcache0 251:0 0 1024M 0 disk
# echo writeback > /sys/block/sda/bcache/cache_mode
# echo 1 > /sys/block/sda/device/delete
[ 85.713826] sd 2:0:0:0: [sda] Synchronizing SCSI cache
# sleep 10
[ 90.428125] bcache: cached_dev_status_update() sda: device offline for 5
seconds
[ 90.431495] bcache: cached_dev_status_update() bdev0: disable I/O request
due to backing device offline
[ 90.435591] bcache: bcache_device_free() bcache0 stopped
#
# lsblk -e 252
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 1G 0 loop
└─fake-loop0 253:0 0 1024M 0 dm
# ls /dev/bcache0
ls: cannot access '/dev/bcache0': No such file or directory
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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/1829563
Title:
bcache: risk of data loss on I/O errors in backing or caching devices
Status in linux package in Ubuntu:
Invalid
Status in linux source package in Bionic:
In Progress
Status in linux source package in Cosmic:
In Progress
Bug description:
[Impact]
* The bcache code in Bionic lacks several fixes to handle
I/O errors in both backing devices and caching devices.
* Partial or permanent errors in backing or caching devices,
specially in writeback mode, can lead to data loss and/or
the application is not notified about failed I/O requests.
* The bcache device might remain available for I/O requests
even if backing device is offline, so writes are undefined.
[Test Case]
* Detailed test cases/steps for the behavior of almost every
patch with code logic changes are provided in bug comments.
* The patchset has been tested for regressions on each cache
mode (writethrough, writeback, writearound, none) with the
xfstests test suite (on ext4), fio (random read-write) and
iozone (several read/write tests).
[Regression Potential]
* The patchset is relatively large and touches several areas
in bcache code, however, synthetic testing of the patches
has been performed, and extensive regression/stress tests
were run (as mentioned in Test Case section).
* Many patches in the patchset are 'Fixes' patches to other
patches, and no further 'Fixes' currently exist upstream.
[Other Info]
* Canonical Field Eng. deploys bcache+writeback extensively
(e.g., BootStack, UA cloud, except rare all-flash cases).
[Original Bug Description]
This is a request for a backport of the following upstream patch from
4.18:
"bcache: stop bcache device when backing device is offline"
https://github.com/torvalds/linux/commit/0f0709e6bfc3ce4e8e1c0e8573490c45f76cfeee
Field engineering uses bcache quite extensively and it would be good
to have this in the GA/bionic kernel.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1829563/+subscriptions
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