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Bug 678562

Summary:	writing to a virtio serial port while no one is listening on the host side hangs the guest [rhel-6.0.z]
Product:	Red Hat Enterprise Linux 6	Reporter:	RHEL Program Management <pm-rhel>
Component:	kernel	Assignee:	Frantisek Hrbata <fhrbata>
Status:	CLOSED ERRATA	QA Contact:	Red Hat Kernel QE team <kernel-qe>
Severity:	medium	Docs Contact:
Priority:	low
Version:	6.0	CC:	amit.shah, dhoward, hdegoede, juzhang, mjenner, plyons, pm-eus, virt-maint
Target Milestone:	rc	Keywords:	ZStream
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	kernel-2.6.32-71.19.1.el6	Doc Type:	Bug Fix
Doc Text:	If a host was slow in reading data or did not read data at all, blocking write() calls not only blocked the program that called the write() call but also the entire guest. This was caused by the write() calls waiting until an acknowledgment that the data consumed was received from the host. With this update, write() calls no longer wait for such acknowledgment: control is immediately returned to the user space application. This ensures that even if the host is busy processing other data or is not consuming data at all, the guest is not blocked.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2011-04-08 02:59:49 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:	643751
Bug Blocks:

Description RHEL Program Management 2011-02-18 12:41:06 UTC

This bug has been copied from bug #643751 and has been proposed
to be backported to 6.0 z-stream (EUS).

Comment 5 juzhang 2011-03-23 06:16:30 UTC

According to comment4,set this issue as verified

Comment 6 errata-xmlrpc 2011-04-08 02:59:49 UTC

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 therefore 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/RHSA-2011-0421.html

Comment 7 Martin Prpič 2011-04-12 12:42:02 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:
If a host was slow in reading data or did not read data at all, blocking write() calls not only blocked the program that called the write() call but also the entire guest. This was caused by the write() calls waiting until an acknowledgment that the data consumed was received from the host. With this update, write() calls no longer wait for such acknowledgment: control is immediately returned to the user space application. This ensures that even if the host is busy processing other data or is not consuming data at all, the guest is not blocked.