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Created attachment 1349997[details]
Console logs
Description of problem:
When creating VDO directly on top of existing VDO, console is spammed with message "kvdo347:dedupeQ: kvdoMapBio called from within a VDO thread!". The VDO is actually succesfully created:
# vdo create --device /dev/mapper/vdo --name vdo2 --verbose
Creating VDO vdo2
modprobe kvdo
vdoformat --uds-checkpoint-frequency=0 --uds-memory-size=0.25 /dev/mapper/vdo
vdodumpconfig /dev/mapper/vdo
Starting VDO vdo2
dmsetup status vdo2
modprobe kvdo
dmsetup create vdo2 --table '0 11721045168 dedupe /dev/mapper/vdo 4096 disabled 0 32768 16380 on sync vdo2 ack=1,bio=4,bioRotationInterval=64,cpu=2,hash=1,logical=1,physical=1'
dmsetup status vdo2
Starting compression on VDO vdo2
dmsetup message vdo2 0 compression on
dmsetup status vdo2
VDO instance 348 volume is ready at /dev/mapper/vdo2
Attaching console log as it is too long.
Using kmod-kvdo component as it is produced by kvdo.
Version-Release number of selected component (if applicable):
vdo 6.1.0.34-8
How reproducible:
100%
Steps to Reproduce:
1.vdo create --device DEVICE --name VDO
2.vdo create --device /dev/mapper/VDO --name VDO2
Actual results:
VDO created, spam in console
Expected results:
Not allowed / no spam
Additional info:
Eliminating the messages entirely isn't a good idea, as they're trying to warn about a potential deadlock situation, but the current test isn't strict enough, and as noted will complain about one VDO device atop another.
There are some relatively easy improvements we could put in: Throttling the messages to once per second would be fairly easy. Having the "vdo" script check the storage device and its slaves recursively (to catch a VDO-LVM-VDO stacking) wouldn't be hard either but updated test cases will take a little time to put together.
Actually making the in-kernel test stricter would be preferable, but will take a while to implement, and there may be a small performance impact for VDO-on-VDO stacking.
Turns out not to have taken as much work as I thought, I just had to add a tiny abstraction break... There shouldn't be a performance impact with the approach I settled on.
Tested with vdo-6.1.0.124 and could not hit the message with VDO on top of VDO.
Before I set this to verified, I would like to try to hit the deadlock situation to see if the message can be triggered. Ken, do you know of any reproducer of such situation?
Thanks
The Permabit perl test suite does have a test that triggers it, called DeadlockAvoidance01 in our suite. It uses a couple custom device-mapper targets to get the behavior we want to test. It might be possible to trigger with only one hand-crafted DM target; I haven't tried rewriting it that way.
Unfortunately I don't have a reproducer without specialized kernel modules.
So the message is gone in the situation mentioned in this BZ and still appears in the test designed to trigger it, so the basic functionality is not gone.
Thanks Ken,
setting to verified.
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://access.redhat.com/errata/RHEA-2018:0900
Created attachment 1349997 [details] Console logs Description of problem: When creating VDO directly on top of existing VDO, console is spammed with message "kvdo347:dedupeQ: kvdoMapBio called from within a VDO thread!". The VDO is actually succesfully created: # vdo create --device /dev/mapper/vdo --name vdo2 --verbose Creating VDO vdo2 modprobe kvdo vdoformat --uds-checkpoint-frequency=0 --uds-memory-size=0.25 /dev/mapper/vdo vdodumpconfig /dev/mapper/vdo Starting VDO vdo2 dmsetup status vdo2 modprobe kvdo dmsetup create vdo2 --table '0 11721045168 dedupe /dev/mapper/vdo 4096 disabled 0 32768 16380 on sync vdo2 ack=1,bio=4,bioRotationInterval=64,cpu=2,hash=1,logical=1,physical=1' dmsetup status vdo2 Starting compression on VDO vdo2 dmsetup message vdo2 0 compression on dmsetup status vdo2 VDO instance 348 volume is ready at /dev/mapper/vdo2 Attaching console log as it is too long. Using kmod-kvdo component as it is produced by kvdo. Version-Release number of selected component (if applicable): vdo 6.1.0.34-8 How reproducible: 100% Steps to Reproduce: 1.vdo create --device DEVICE --name VDO 2.vdo create --device /dev/mapper/VDO --name VDO2 Actual results: VDO created, spam in console Expected results: Not allowed / no spam Additional info: