Bug 665227

Summary: Entering screen to copy/scrollback mode caused guest deadlock
Product: Red Hat Enterprise Linux 6 Reporter: Amos Kong <akong>
Component: qemu-kvmAssignee: Gerd Hoffmann <kraxel>
Status: CLOSED WONTFIX QA Contact: Virtualization Bugs <virt-bugs>
Severity: medium Docs Contact:
Priority: medium    
Version: 6.1CC: ailan, alex.williamson, mkenneth, mzhan, tburke, virt-maint
Target Milestone: rcKeywords: Upstream
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of: 664635 Environment:
Last Closed: 2011-06-01 15:57:12 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:
Bug Depends On: 664635    
Bug Blocks: 580953    

Comment 3 Gerd Hoffmann 2011-06-01 15:57:12 UTC 
As Eduardo sayed in bug 664635:

Just don't stop reading data, this is asking for trouble.

We could try to fix that by implementing flow control everythere, so the guest gets signaled via serial port status registers that the pipe is full and stops writing more.  This depends on pimping up qemu chardevs, which in turn depends on glib main loop, which pretty much implies it is RHEL-7 material.

I suspect that still wouldn't help much for linux kernel messages as the serial console writes are done syncronously.  You can see that even on bare metal, configure a serial line with 9600 baud and watch how this slows down the kernel boot.  In the end qemu wouldn't block, but the linux kernel would block instead.