Bug 950002

Summary:	vhost_net experimental_zcopytx enable crashes VMs
Product:	[Fedora] Fedora	Reporter:	David Carlson <thecubic>
Component:	kernel	Assignee:	Michael S. Tsirkin <mst>
Status:	CLOSED ERRATA	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	medium	Docs Contact:
Priority:	unspecified
Version:	18	CC:	gansalmon, itamar, jasowang, jonathan, kernel-maint, madhu.chinakonda
Target Milestone:	---
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Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2013-09-20 19:04:43 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 David Carlson 2013-04-09 12:54:09 UTC

Description of problem:
guest VM qemu processes will occasionally become defunct (requiring host restart) due to the enabling of experimental_zcopytx in the vhost_net module when using macvtap

Version-Release number of selected component (if applicable):
kernel-3.8.5-201.fc18.x86_64

How reproducible:
Use a KVM Windows 7 VM with macvtap & bridging (vhost_net driver) + netkvm, run network traffic and/or attempt to restart the guest

Actual results:
guest transfers network data / restarts without kernel warning and defunctness

Expected results:
kernel warning, defunct process
(abrt reports: https://retrace.fedoraproject.org/faf/reports/69052/)
(see the abrt BZ ticket: https://bugzilla.redhat.com/show_bug.cgi?id=918015)

Additional info:
The problem appears to be solved for me by adding

/etc/modprobe.d/vhost_net.conf:
options vhost_net experimental_zcopytx=0

...maybe the option should be distribution-disabled?

Comment 2 Josh Boyer 2013-09-20 19:04:43 UTC

I believe this was fixed via other bugs in newer kernels.  If you are still having troubles with this on the latest F18/F19 kernel, please reopen.