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Message #68770
[Bug 1064521] Re: Kernel I/O scheduling writes starving reads, local DoS
** Changed in: linux (Ubuntu Quantal)
Status: Triaged => Won't Fix
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https://bugs.launchpad.net/bugs/1064521
Title:
Kernel I/O scheduling writes starving reads, local DoS
Status in “linux” package in Ubuntu:
Triaged
Status in “linux” source package in Precise:
Triaged
Status in “linux” source package in Quantal:
Won't Fix
Bug description:
On the Precise default kernel, it is possible by executing zcat on a
large file for an unprivileged user to disrupt I/O sufficiently that
it causes serious disruption.
Serious disruption means (e.g.) a single MySQL update hangs for over
120 seconds on the default scheduler (cfq), and between 1 and 11
seconds on the deadline scheduler.
This is reproducible on 2 sets of hardware using:
root@extility-qa-test:~# uname -a
Linux extility-qa-test 3.2.0-29-generic #46-Ubuntu SMP Fri Jul 27 17:03:23 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
linux-image-3.2.0-29-generic 3.2.0-29.46
root@extility-qa-test:~# cat /proc/sys/vm/dirty_ratio
20
root@extility-qa-test:~# cat /proc/sys/vm/dirty_background_ratio
10
No such problems occur on Lucid OS running the Oneiric Backports
kernel.
root@management-dev2:~# uname -a
Linux management-dev2 3.0.0-15-server #26~lucid1-Ubuntu SMP Wed Jan 25 15:55:45 UTC 2012 x86_64 GNU/Linux
linux-image-3.0.0-15-server 3.0.0-15.26~lucid1
In order to replicate, download (e.g.) this gzipped Lucid image (note this is not the OS we are running, this is just an example of the a file that causes the problem):
http://repo.flexiant.com/images/public/kvm/ubuntu10.04.img.gz
and as un unprivileged user, on a default, untuned Precise install, do
zcat ubuntu10.04.img.gz > test
Now in another window execute any trivial mysql update on any table. Note that this can take a hugely long time.
"show full processlist" in mysql console will show the time taken
executing the command.
In kernel logs (with cfq) we see e.g.:
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268048] INFO: task mysqld:1358 blocked for more than 120 seconds.
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268144] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268267] mysqld D ffffffff81806200 0 1358 1 0x00000000
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268272] ffff8801921fde48 0000000000000082 ffff8801921fde00 0000000300000001
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268278] ffff8801921fdfd8 ffff8801921fdfd8 ffff8801921fdfd8 0000000000013780
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268283] ffff880195169700 ffff880191f79700 ffff8801921fde58 ffff8801912b2800
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268288] Call Trace:
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268298] [<ffffffff816579cf>] schedule+0x3f/0x60
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268303] [<ffffffff812650d5>] jbd2_log_wait_commit+0xb5/0x130
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268308] [<ffffffff8108aa50>] ? add_wait_queue+0x60/0x60
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268313] [<ffffffff81211248>] ext4_sync_file+0x208/0x2d0
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268317] [<ffffffff81177ba0>] ? vfs_write+0x110/0x180
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268321] [<ffffffff811a63a6>] do_fsync+0x56/0x80
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268325] [<ffffffff811a66d0>] sys_fsync+0x10/0x20
Oct 8 14:57:02 extility-qa-test kernel: [ 3840.268329] [<ffffffff81661ec2>] system_call_fastpath+0x16/0x1b
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268176] INFO: task mysqld:1358 blocked for more than 120 seconds.
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268282] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268393] mysqld D ffffffff81806200 0 1358 1 0x00000000
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268399] ffff8801921fde48 0000000000000082 ffff8801921fde00 0000000300000001
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268405] ffff8801921fdfd8 ffff8801921fdfd8 ffff8801921fdfd8 0000000000013780
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268410] ffff880195169700 ffff880191f79700 ffff8801921fde58 ffff8801912b2800
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268415] Call Trace:
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268426] [<ffffffff816579cf>] schedule+0x3f/0x60
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268431] [<ffffffff812650d5>] jbd2_log_wait_commit+0xb5/0x130
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268436] [<ffffffff8108aa50>] ? add_wait_queue+0x60/0x60
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268441] [<ffffffff81211248>] ext4_sync_file+0x208/0x2d0
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268445] [<ffffffff81177ba0>] ? vfs_write+0x110/0x180
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268450] [<ffffffff811a63a6>] do_fsync+0x56/0x80
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268454] [<ffffffff811a66d0>] sys_fsync+0x10/0x20
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268458] [<ffffffff81661ec2>] system_call_fastpath+0x16/0x1b
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268473] INFO: task master:1525 blocked for more than 120 seconds.
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.268563] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
This isn't just a problem with MySQL. Here it is killing Postgres:
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269090] INFO: task postgres:2188 blocked for more than 120 seconds.
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269188] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269298] postgres D ffffffff81806200 0 2188 2186 0x00000000
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269302] ffff8801919cbe48 0000000000000082 ffff8801919cbe00 0000000300000001
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269307] ffff8801919cbfd8 ffff8801919cbfd8 ffff8801919cbfd8 0000000000013780
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269312] ffff880195169700 ffff8801916fae00 ffff8801919cbe58 ffff8801912b2800
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269317] Call Trace:
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269321] [<ffffffff816579cf>] schedule+0x3f/0x60
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269325] [<ffffffff812650d5>] jbd2_log_wait_commit+0xb5/0x130
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269328] [<ffffffff8108aa50>] ? add_wait_queue+0x60/0x60
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269332] [<ffffffff81211248>] ext4_sync_file+0x208/0x2d0
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269335] [<ffffffff81177ba0>] ? vfs_write+0x110/0x180
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269339] [<ffffffff811a63a6>] do_fsync+0x56/0x80
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269342] [<ffffffff811a66d0>] sys_fsync+0x10/0x20
Oct 8 14:59:02 extility-qa-test kernel: [ 3960.269346] [<ffffffff81661ec2>] system_call_fastpath+0x16/0x1b
Standard information follows:
root@extility-qa-test:~# lsb_release -rd
Description: Ubuntu 12.04.1 LTS
Release: 12.04
root@extility-qa-test:~# apt-cache policy linux-image-3.2.0-29-generic
linux-image-3.2.0-29-generic:
Installed: 3.2.0-29.46
Candidate: 3.2.0-29.46
Version table:
*** 3.2.0-29.46 0
500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
500 http://security.ubuntu.com/ubuntu/ precise-security/main amd64 Packages
100 /var/lib/dpkg/status
Expected behaviour: same as Lucid, perhaps MySQL slows down a bit, but
cannot be DoS'd
What actually happened: local DoS of MySQL.
---
AlsaDevices:
total 0
crw-rw---T 1 root audio 116, 1 Oct 9 10:02 seq
crw-rw---T 1 root audio 116, 33 Oct 9 10:02 timer
AplayDevices: Error: [Errno 2] No such file or directory
ApportVersion: 2.0.1-0ubuntu13
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
CRDA: Error: [Errno 2] No such file or directory
DistroRelease: Ubuntu 12.04
HibernationDevice: RESUME=UUID=5cd80c3d-3646-42ed-bf16-528a0151228d
InstallationMedia: Ubuntu-Server 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120817.3)
IwConfig: Error: [Errno 2] No such file or directory
MachineType: Dell Inc. PowerEdge R210 II
Package: linux (not installed)
PciMultimedia:
ProcEnviron:
LANGUAGE=en_GB:en
TERM=xterm-color
LANG=en_GB.UTF-8
SHELL=/bin/bash
ProcFB: 0 VESA VGA
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-29-generic root=UUID=9daecda1-1f0f-41a0-91b8-5981fdea5c9e ro quiet
ProcVersionSignature: Ubuntu 3.2.0-29.46-generic 3.2.24
RelatedPackageVersions:
linux-restricted-modules-3.2.0-29-generic N/A
linux-backports-modules-3.2.0-29-generic N/A
linux-firmware 1.79
RfKill: Error: [Errno 2] No such file or directory
Tags: precise
Uname: Linux 3.2.0-29-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:
dmi.bios.date: 03/13/2012
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 2.0.5
dmi.board.name: 03X6X0
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 23
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr2.0.5:bd03/13/2012:svnDellInc.:pnPowerEdgeR210II:pvr:rvnDellInc.:rn03X6X0:rvrA00:cvnDellInc.:ct23:cvr:
dmi.product.name: PowerEdge R210 II
dmi.sys.vendor: Dell Inc.
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