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Bug 1316287

Summary:	Possible QEMU deadlock after creating image snapshots
Product:	[Red Hat Storage] Red Hat Ceph Storage	Reporter:	Jason Dillaman <jdillama>
Component:	RBD	Assignee:	Jason Dillaman <jdillama>
Status:	CLOSED ERRATA	QA Contact:	Tejas <tchandra>
Severity:	medium	Docs Contact:	Bara Ancincova <bancinco>
Priority:	unspecified
Version:	1.3.2	CC:	ceph-eng-bugs, flucifre, hnallurv, icolle, jdillama, kdreyer, nlevine
Target Milestone:	rc
Target Release:	1.3.3
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	RHEL: ceph-0.94.7-5.el7cp Ubuntu: ceph_0.94.7-3redhat1trusty	Doc Type:	Bug Fix
Doc Text:	.The QEMU process no longer hangs when creating snapshots on images When the RADOS Block Device (RBD) cache was enabled, creating a snapshot on an image with active I/O operations could cause the QEMU process to become unresponsive. With this update, the QEMU process no longer hangs in the described scenario.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2016-09-29 12:57:02 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:
Bug Depends On:	1335269
Bug Blocks:	1372735

Description Jason Dillaman 2016-03-09 21:41:39 UTC

Description of problem:
Creating a snapshot out-of-band (e.g. rbd snap create image@snap) on an image with active IO might result in all IO hanging within the QEMU process.  This only occurs when the RBD cache is enabled.

Version-Release number of selected component (if applicable):
1.3.2

How reproducible:
Requires that the RBD cache have pending writeback IO when a snapshot is created.

Steps to Reproduce:
1. Start a write-intensive operation within a VM
2. Create a snapshot of the RBD image

Actual results:
QEMU IO will hang

Expected results:
QEMU IO continues without issue

Additional info:

Comment 2 Jason Dillaman 2016-03-23 12:02:06 UTC

This issue only affects 1.3.x -- it doesn't affect 2.0.  Resetting the flags to account for the change.

Comment 3 Ken Dreyer (Red Hat) 2016-08-02 20:16:18 UTC

Fixed in v0.94.7 upstream. We'll take this BZ as part of the rebase (bz 1335269).

Comment 8 Tejas 2016-09-12 10:39:58 UTC

Verified in ceph version:
ceph version 0.94.9-1.el7cp

Steps followed:
1. enable rbd caching.
2. attach a RBD image to a KVM instance.
3. start IO on the RBD image from the VM.
4. Take  snapshots of the RBD image.
5. clone a snapshot.

No imapct to IO.

Moving this to Verified.

Thanks,
Tejas

Comment 11 errata-xmlrpc 2016-09-29 12:57:02 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.

https://rhn.redhat.com/errata/RHSA-2016-1972.html