RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.
Bug 805533 - qemu-ga: possible race while suspending the guest
Summary: qemu-ga: possible race while suspending the guest
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: qemu-kvm
Version: 6.3
Hardware: All
OS: Linux
high
high
Target Milestone: rc
: ---
Assignee: Luiz Capitulino
QA Contact: Virtualization Bugs
URL:
Whiteboard:
Depends On:
Blocks: 804161 831387
TreeView+ depends on / blocked
 
Reported: 2012-03-21 14:27 UTC by Luiz Capitulino
Modified: 2013-10-15 14:08 UTC (History)
11 users (show)

Fixed In Version: qemu-kvm-0.12.1.2-2.307.el6
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2013-02-21 07:33:16 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2013:0527 0 normal SHIPPED_LIVE qemu-kvm bug fix and enhancement update 2013-02-20 21:51:08 UTC

Description Luiz Capitulino 2012-03-21 14:27:41 UTC 
During qemu-ga patch review it was found that there's a possible race in the code used to detect if the guest supports suspend. No suspend support could be erroneously reported when the race is triggered.

The code in question is in bios_supports_mode() function. Theoretically, the following calls could be interrupted if one of the children created by bios_supports_mode() exits - or other children created by qemu-ga, although no other code that could run in parallel with bios_supports_mode() does that today:

 close(pipefds[1]);
 g_free(pmutils_path);

 ret = read(pipefds[0], &status, sizeof(status));

The quick & easy solution for RHEL6.3 is to loop read() on EINTR error and block SIGCHLD during the close() and g_free() functions.

The Right solution for upstream is to add a general interface to create & safely wait for children to terminate. This would also simplify the suspend functions.
Comment 1 Ademar Reis 2012-04-09 23:53:37 UTC 
Corner case on a tech-preview feature, postponing to 6.4.
Comment 2 Luiz Capitulino 2012-04-10 14:47:07 UTC 
Took this upstream and the recommendation is to implement the easy fix:

  http://lists.gnu.org/archive/html/qemu-devel/2012-04/msg00998.html

This is doable for 6.3, but I agree it's a corner case.
Comment 3 Luiz Capitulino 2012-05-16 20:18:14 UTC 
After some discussion, we decided to make the guest-suspend-* commands synchronous. This just drops the need for the SIGCHLD signal, which automatically ends up fixing this issue.

Patches submitted some days ago and already included in Michael Roth's latest pull request:

http://lists.gnu.org/archive/html/qemu-devel/2012-05/msg02093.html
Comment 10 Luiz Capitulino 2012-11-29 12:29:41 UTC 
As far as testing is concerned, this issue was found in code review and is theoretical. There's no recipe to trigger it. So I think verification should be skipped.
Comment 11 juzhang 2012-12-03 05:35:25 UTC 
Checked on qemu-kvm-0.12.1.2-2.337.el6, the codes indeed included according to changelog.

#rpm -q qemu-kvm-0.12.1.2-2.337.el6 --changelog | grep 805533
- Update information: Add bug 805533 information to changelog (fix for 827612 fixed also 805533)
- Resolves: bz#805533
Comment 13 errata-xmlrpc 2013-02-21 07:33:16 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2013-0527.html
Comment 14 Qian Guo 2013-10-15 07:42:21 UTC 
Hi, Luiz

Do we need  clone this bug to RHEL7 product?

Thanks
Comment 15 Luiz Capitulino 2013-10-15 14:08:22 UTC 
No, this is a very old issue fixed since qemu v1.1.0, but thanks for checking.
Note You need to log in before you can comment on or make changes to this bug.