Bug 243884
| Summary: | Race in vfb/vkbd device setup | ||
|---|---|---|---|
| Product: | Red Hat Enterprise Linux 5 | Reporter: | Markus Armbruster <armbru> |
| Component: | xen | Assignee: | Markus Armbruster <armbru> |
| Status: | CLOSED ERRATA | QA Contact: | |
| Severity: | low | Docs Contact: | |
| Priority: | low | ||
| Version: | 5.0 | CC: | xen-maint |
| Target Milestone: | --- | ||
| Target Release: | --- | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | RHEA-2007-0635 | Doc Type: | Bug Fix |
| Doc Text: | Story Points: | --- | |
| Clone Of: | Environment: | ||
| Last Closed: | 2007-11-07 17:10:45 UTC | Type: | --- |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
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. This is now built into xen-3.0.3-29.el5 in dist-5E-qu-candidate. An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on the solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHEA-2007-0635.html |
Description of problem: Fixed in xen-unstable cset 14926. Quoting its log message: 1. XendDomainInfo._createDevices() gets a list of devices to be created from XendConfig.ordered_device_refs(). On a simple guest, this has 4 devices, vfb, vbd, vif, vkbd - in that order. 2. It iterates over those devices, creating the appropriate DevController subclass instance, and then calling createDevice() on that object. 3. When createDevice() is called on the vfb device, it spawns xen-vncfb daemon. 4. During startup xen-vncfb writes into the backend paths /local/domain/0/backend/vfb/0 And /local/domain/0/backend/vkbd/0 5. When createDevice() is called on the vkbd device in XenD, if the 2nd xenstore path write from step 4 has occurred, then you'll hit the 'Device 0 (vkbd) is already connected' error. If the 2nd path write didn't complete yet then everything is fine. I think the reason it often works once after boot is that loading xen-vncfb from disk the first time around is just enough of a slow down to ensure step 5 occurs before the 2nd xenstore write in step 4 has occurred. The key seems to be to ensure the vkbd device is initialized in xenstore before the vfb device - this ensures all the xenstored setup from XenD is complete before the xen-vncfb daemon starts. I'm now able to create & destroy a domain many times over with this patch & never hit the error message any more. End quote. The order in which devices are created is non-random but unpredictable; small, innocent-looking changes to the xend code can change the order, as can a Python upgrade. With the current xend code and Python, vkbd is created before vfb, and therefore the bug can't bite. How reproducible: Not reproducible with the current version. Actual results: If it were reproducible, xend would complain: Device 0 (vkbd) is already connected and refuse to create the vkbd device, which breaks the pvfb. Expected results: Device is created, pvfb works. Additional info: