Bug 824909

Summary:	util-linux-2.20.1-2.3 breaks lxc containers that share their host root file system and create pseudo tty instances
Product:	[Fedora] Fedora	Reporter:	Steven Galgano <sgalgano>
Component:	lxc	Assignee:	Thomas Moschny <thomas.moschny>
Status:	CLOSED WORKSFORME	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	16	CC:	jonathan, karlthered, kzak, mluscon, thomas.moschny
Target Milestone:	---
Target Release:	---
Hardware:	Unspecified
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2012-08-04 12:31:49 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Steven Galgano 2012-05-24 15:01:50 UTC

Description of problem:
The addition of the 'MS_REC' flag in the util-linux-2.20-mount-rec.patch used in util-linux-2.20.1-2.3 breaks lxc containers that share their host root file system and create pseudo tty instances.

Version-Release number of selected component (if applicable):
util-linux-2.20.1-2.3
lxc-0.7.5-1

How reproducible:
Can be reproduced on demand.

Steps to Reproduce:
1. Create a 'lxc.conf' file containing the following single line:
lxc.pts = 128
2. Issue the following command to create a container running a bash shell:
$ sudo lxc-execute -f lxc.conf --name test bash

Actual results:
$ sudo lxc-execute -f lxc.conf --name test bash
lxc-execute: Device or resource busy - failed to umount 'dev/pts'
lxc-execute: failed to setup the new pts instance
lxc-execute: failed to setup the container
lxc-execute: invalid sequence number 1. expected 2
lxc-execute: failed to spawn 'test'

Expected results:
$ sudo lxc-execute -f lxc.conf --name test bash
[root@demo ~]#

Additional info:
I downgraded to the previous version of util-linux (2.20.1-2) in order to trace the problem back to a specific package. After running some tests I isolated the issue to the inclusion of the util-linux-2.20-mount-rec.patch in util-linux-2.20.1-2.3 which was not present in util-linux-2.20.1-2.

Removing the patch from the spec file or modifying the patch to not include the 'MS_REC' flags, which is effectively the same as removing the patch, remedies the issue.

I do not have enough knowledge of libmount to understand the purpose of the patch or how it relates to lxc usage of /dev/pts.

Comment 1 Karel Zak 2012-07-17 13:03:41 UTC

The MS_REC flag is required for recursive mount operations -- for example --rbind, --make-rshare, etc.

It seems that something in lxc containers depends on the old *broken* implementation where MS_REC has been incorrectly removed. 

It would be nice to identify the mount usage (or command) in lxc with 
MS_SHARED, MS_SLAVE, MS_UNBINDABLE or MS_PRIVATE operations.

The util-linux-2.20-mount-rec.patch cannot be removed.

Comment 2 Thomas Moschny 2012-07-17 16:42:08 UTC

On Fedora 17/x86_64, I cannot reproduce the problem:

# rpm -q lxc lxc-libs util-linux
lxc-0.7.5-1.fc17.x86_64
lxc-libs-0.7.5-1.fc17.x86_64
util-linux-2.21.2-2.fc17.x86_64

# uname -r
3.4.4-5.fc17.x86_64

# echo "lxc.pts = 128" > /tmp/lxc.conf
# lxc-execute -f /tmp/lxc.conf --name test /usr/bin/bash
# ps ax
  PID TTY      STAT   TIME COMMAND
    1 ?        S      0:00 /usr/lib64/lxc/lxc-init -- /usr/bin/bash
    2 ?        S      0:00 /usr/bin/bash
  214 ?        R+     0:00 ps ax


As far as I can see, lxc uses MS_REC only while mounting the rootfs (in src/lxc/conf.c):

static int mount_rootfs_dir(const char *rootfs, const char *target)
{
	return mount(rootfs, target, "none", MS_BIND | MS_REC, NULL);
}

Comment 3 Thomas Moschny 2012-07-27 17:02:42 UTC

Need more information on how to reproduce and possibly report this upstream.

Comment 4 Thomas Moschny 2012-08-04 12:31:49 UTC

Also cannot reproduce on F16/x86_64:

# rpm -q lxc lxc-libs util-linux
lxc-0.7.5-1.fc16.x86_64
lxc-libs-0.7.5-1.fc16.x86_64
util-linux-2.20.1-2.3.fc16.x86_64
# uname -r
3.4.4-4.fc16.x86_64
# echo "lxc.pts = 128" > /tmp/lxc.conf
# lxc-execute -f /tmp/lxc.conf --name test /bin/bash
# ps ax
  PID TTY      STAT   TIME COMMAND
    1 ?        S      0:00 /usr/lib64/lxc/lxc-init -- /bin/bash
    2 ?        S      0:00 /bin/bash
   94 ?        R+     0:00 ps ax

So, closing.