fio crashes when using --offset with a device

[Mark Lehrer]

e.g. here is how I was running it:

fio --loops=1 --direct=1 --rw=write --ioengine=libaio --bs=4K --iodepth=16 --numjobs=1 --time_based --runtime=10 --group_reporting --size=10% --offset=10% --name=TEST --filename=/dev/nvme0n1

I built the 3.17 source and the problem didn't happen. If you can't bump the universe version to 3.21 or 3.17 and need a patch for 3.16, I can make one for you if necessary.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: fio 3.16-1
ProcVersionSignature: Ubuntu 5.4.0-37.41-generic 5.4.41
Uname: Linux 5.4.0-37-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.6
Architecture: amd64
CasperMD5CheckResult: pass
Date: Tue Aug 11 13:14:24 2020
InstallationDate: Installed on 2020-05-19 (84 days ago)
InstallationMedia: Ubuntu-Server 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: fio
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Joel Colledge (jcolledge)]

I have also observed strange behavior with the fio 3.16 package on Focal. It occurs with the combination of "size" and "offset", and is affected by the presence of "time_based".

For example with this command:

fio --name=test --filename=/dev/loop9 --ioengine=libaio --rw=write --direct=1 --offset=8M --size=8M --time_based --runtime=2

I observe that the device is written from 8M to the end. I have tested with a range of other fio versions and they all write from 8M to 16M as expected.

It looks like the issue was introduced with https://github.com/axboe/fio/commit/ad46c5715ffc5d4e70d2e941225b1f504f23e409
This commit was reverted in https://github.com/axboe/fio/commit/0d0601479d593ca9e96e35f43e2c0586f8358f34
The only fio version containing the original commit but not the revert is 3.16.

I have not experienced this exact failure but it seems very likely to have the same root cause.