I/O Error Test 7
================
commit: "bcache: fix ioctl in flash device"
This test needs QEMU+GDB since there's no way to set the variable
from the kernel, because it references incorrect memory/pointer.
In the original kernel, the ioctl() to a flash-only volume
goes from ioctl_dev() down to flash_dev_ioctl()
(which always return -ENOTTY always) only if its backing device
has io_disable == 0, but gets -EIO if io_disable == 1
(which are both wrong as flash device has no backing device).
In the modified kernel, it always go down to flash_dev_ioctl(),
thus -ENOTTY in both cases.
Original kernel:
$ uname -rv
4.15.0-51-generic #55-Ubuntu SMP Wed May 15 14:27:21 UTC 2019
io_disable = 0:
# ./ioctl
ioctl: Inappropriate ioctl for device
io_disable = 1:
# ./ioctl
ioctl: Input/output error
Modified kernel:
# uname -rv
4.18.0-23-generic #24+test20190619b1 SMP Wed Jun 19 22:33:22 UTC 2019
io_disable = 0:
# ./ioctl
ioctl: Inappropriate ioctl for device
io_disable = 1:
# ./ioctl
ioctl: Inappropriate ioctl for device
Steps
-----
$ sudo -i
# ./setup.sh >/dev/null 2>&1
[ 57.607391] bcache: register_bdev() registered backing device dm-0
[ 57.611885] bcache: run_cache_set() invalidating existing data
[ 57.625712] bcache: register_cache() registered cache device dm-1
[ 58.605153] bcache: bch_cached_dev_attach() Caching dm-0 as bcache0 on set
08f1756b-081f-4545-a947-927d429f7ef1
# 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
loop1 7:1 0 1G 0 loop
└─fake-loop1 253:1 0 1024M 0 dm
└─bcache0 251:0 0 1024M 0 disk
# echo $((128*1024**2)) > /sys/block/dm-1/bcache/set/flash_vol_create
# 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
loop1 7:1 0 1G 0 loop
└─fake-loop1 253:1 0 1024M 0 dm
├─bcache0 251:0 0 1024M 0 disk
└─bcache1 251:128 0 128M 0 disk
# ls -1d /sys/block/bcache1/bcache/cache/volume*
/sys/block/bcache1/bcache/cache/volume1
# cat /sys/module/bcache/sections/.text
0xffffffffc05f4000
# cat ioctl.c
#include <sys/ioctl.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
int main() {
int fd, rc;
fd = open("/dev/bcache1", O_RDWR);
if (fd == -1) {
perror("open");
return 0;
}
rc = ioctl(fd, 0xcc00ffee); // our cookie.
if (rc == -1)
perror("ioctl");
close(fd);
return 0;
}
# gcc -o ioctl ioctl.c
# ./ioctl
(gdb) add-symbol-file
~/ddeb-4.18.0-23-generic/usr/lib/debug/lib/modules/4.18.0-23-generic/kernel/drivers/md/bcache/bcache.ko
0xffffffffc05f4000
(gdb) b *ioctl_dev +0x13
(gdb) c
Thread 4 hit Breakpoint 1, ioctl_dev (b=<optimized out>, mode=134610975,
cmd=3422617582, arg=2) at
/build/linux-JHFGaE/linux-4.18.0/drivers/md/bcache/super.c:641
...
(gdb) p/x 3422617582
$53 = 0xcc00ffee // our cookie.
(gdb) print d.name
$54 = "volume1\000\000\000\000" // matches the volume above.
See it's an incorrect pointer.
No way to set it via any io_disable in sysfs.
(gdb) print ((struct cached_dev *)((void *)d - 0x10)).backing_dev_name
$75 =
"\017\000\000\000\260\373\212s\277\230\377\377\260\373\212s\277\230\377\377
nԇ\377\377\377\377\060qh\211"
(gdb) print ((struct cached_dev *)((void *)d - 0x10)).io_disable
$76 = 0
With the default value (io_disable = 0):
# ./ioctl
ioctl: Inappropriate ioctl for device
(gdb) c
... repeat.
With the forced value (io_disable = 1):
(gdb) set ((struct cached_dev *)((void *)d - 0x10)).io_disable = 1
(gdb) c
# ./ioctl
ioctl: Input/output error
--
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 many patches
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) and fio (sequential + random
read-write).
[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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