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Bug 712653 - make guest mode entry to be rcu quiescent state
Summary: make guest mode entry to be rcu quiescent state
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: kernel
Version: 6.2
Hardware: All
OS: Linux
urgent
high
Target Milestone: rc
: ---
Assignee: Gleb Natapov
QA Contact: Virtualization Bugs
URL:
Whiteboard:
Depends On:
Blocks: 740352
TreeView+ depends on / blocked
 
Reported: 2011-06-12 07:50 UTC by Gleb Natapov
Modified: 2018-11-14 18:52 UTC (History)
7 users (show)

Fixed In Version: kernel-2.6.32-160.el6
Doc Type: Bug Fix
Doc Text:
When a CPU is about to modify data protected by the RCU (Read Copy Update) mechanism, it has to wait for other CPUs in the system to pass a quiescent state. Previously, the guest mode was not considered a quiescent state. As a consequence, if a CPU was in the guest mode for a long time, another CPU had to wait a long time in order to modify RCU-protected data. With this update, the rcu_virt_note_context_switch() function, which marks the guest mode as a quiescent state, has been added to the kernel, thus resolving this issue.
Clone Of:
Environment:
Last Closed: 2011-12-06 13:38:43 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2011:1530 0 normal SHIPPED_LIVE Moderate: Red Hat Enterprise Linux 6 kernel security, bug fix and enhancement update 2011-12-06 01:45:35 UTC

Description Gleb Natapov 2011-06-12 07:50:39 UTC 
KVM does not hold any references to rcu protected data when it switches
CPU into a guest mode. In fact switching to a guest mode is very similar
to exiting to userspase from rcu point of view. In addition CPU may stay
in a guest mode for quite a long time (up to one time slice). Lets treat
guest mode as quiescent state, just like we do with user-mode execution.
Comment 2 RHEL Program Management 2011-06-13 16:10:21 UTC 
This request was evaluated by Red Hat Product Management for inclusion
in a Red Hat Enterprise Linux maintenance release. Product Management has 
requested further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed 
products. This request is not yet committed for inclusion in an Update release.
Comment 3 juzhang 2011-06-16 07:51:33 UTC 
Tested on 2.6.32-156.el6.x86_64 with qemu-kvm-0.12.1.2-2.165.el6.x86_64, marked as qa_ack+

steps
1. boot guest with virtio devices and vcpu=4
2. in guest
#halt

Result:
guest just pause for a couple of seconds after printing "Disabling non-boot CPUs"

Please note:
guest should be rhel6.X
Comment 4 Aristeu Rozanski 2011-06-27 19:04:43 UTC 
Patch(es) available on kernel-2.6.32-160.el6
Comment 10 juzhang 2011-10-13 05:18:13 UTC 
Verified this issue on kernel 2.6.32-206.el6.x86_64 with qemu-kvm-0.12.1.2-2.195.el6.x86_64.,I tried three times.

1.boot guest with boot guest with virtio devices and vcpu=4
2.in guest
#half

Results:
No pause after printing "Disabling non-boot
CPUs"




Guest kernel
2.6.32-206.el6.x86_64
Comment 11 juzhang 2011-10-13 05:19:02 UTC 
According to comment3 and comment10,set this issue as verified.
Comment 12 Tomas Capek 2011-11-23 15:25:58 UTC 
    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
When a CPU is about to modify data protected by the RCU (Read Copy Update) mechanism, it has to wait for other CPUs in the system to pass a quiescent state. Previously, the guest mode was not considered a quiescent state. As a consequence, if a CPU was in the guest mode for a long time, another CPU had to wait a long time in order to modify RCU-protected data. With this update, the rcu_virt_note_context_switch() function, which marks the guest mode as a quiescent state, has been added to the kernel, thus resolving this issue.
Comment 13 errata-xmlrpc 2011-12-06 13:38:43 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/RHSA-2011-1530.html
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