Bug 192924 - FC5 lvcreate -s dosen't create snapshot, but create normal lv
Summary: FC5 lvcreate -s dosen't create snapshot, but create normal lv
Alias: None
Product: Fedora
Classification: Fedora
Component: lvm2   
(Show other bugs)
Version: 5
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Alasdair Kergon
QA Contact:
Depends On:
TreeView+ depends on / blocked
Reported: 2006-05-24 09:22 UTC by Kazutoshi Morioka
Modified: 2007-11-30 22:11 UTC (History)
4 users (show)

Fixed In Version: kernel 2.6.18
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2006-09-26 07:15:42 UTC
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description Kazutoshi Morioka 2006-05-24 09:22:43 UTC
Description of problem:
FC5 lvcreate -s dosen't create snapshot with this error
# lvcreate -L1G -n test myvg
  Logical volume "test" created

This created /dev/myvg/snap is not a snapshot, but a
normal logical volume.
# lvcreate -s -L 500M -n snap /dev/myvg/test
  LV myvg/snap in use: not deactivating
  Couldn't deactivate new snapshot.
# lvs
  LV   VG   Attr   LSize   Origin Snap%  Move Log Copy%
  snap myvg -wi-a- 500.00M
  test myvg -wi-a-   1.00G

After origin-lv was deactivated, and sync,
then the snapshot was created successfully
# lvremove /dev/myvg/snap
Do you really want to remove active logical volume "snap"? [y/n]: y
  Logical volume "snap" successfully removed
# lvchange -a n /dev/myvg/test
# sync ; sync ; sync
# lvcreate -s -L 500M -n snap /dev/myvg/test
  Logical volume "snap" created
# lvs
  LV   VG   Attr   LSize   Origin Snap%  Move Log Copy%
  snap myvg swi--- 500.00M test
  test myvg owi---   1.00G

Version-Release number of selected component (if applicable):
from kernel-2.6.15-1.2054_FC5 to kernel-2.6.16-1.2122_FC5

How reproducible:

Steps to Reproduce:
1. lvcreate -L1G -n test VGNAME
2. lvcreate -s -L 500M -n snap /dev/VGNAME/test
Actual results:
this error was shown and normal lv was created.
"LV myvg/snap in use: not deactivating
  Couldn't deactivate new snapshot."

Expected results:
a snapshot of origin lv was created.

Additional info:
On Fedora Core 4, a snapshot was created successfully
with kernel-2.6.16-1.2111_FC4.i686 and lvm2-2.02.06.

Comment 1 Kazutoshi Morioka 2006-05-24 12:27:58 UTC
I tested first on my PC with Celeron 950MHz.
This box always shows this problem.
I also tested on my another PC with Athlon 64 3000.
On this faster PC also shows this problem, but a bit harder to reproduce.
The problem never occurs when idle state.
But while I was running "badblocks -vv /dev/hda", the problem occurs constantly.

I compiled 2.6.16-1.2122_FC5 with gcc32:
Linux version 2.6.16-1.2122_FC5.gcc32 (morioka@curry.local) (gcc version 3.2.3
20030502 (Red Hat Linux 3.2.3-55.fc5)) #1 Wed May 24 20:35:25 JST 2006
And this kernel also shows same problem.

Comment 2 Alasdair Kergon 2006-06-02 14:54:43 UTC
There've been some reports of similar problems on Debian, apparently related to
udev - we think udev might be holding a reference on the device at the instant
lvm2 tries to remove it causing the removal to fail.  [lvm2 temporarily
activates the 'cow' device to fill the start of it with zeros]

There are also some kernel device-mapper patches upstream (scheduled for 2.6.18
when it opens - currently in -mm) that deal with some races on device creation
and might help.

Comment 3 Kazutoshi Morioka 2006-06-02 15:35:02 UTC
I confirmed that after "udevcontrol stop_exec_queue",
snapshot was always created successfully. Thanks.
This can be an effective workaround.

# udevcontrol stop_exec_queue
# lvcreate -s -L 500M -n snap /dev/VGNAME/test
# udevcontrol start_exec_queue

Comment 4 Kazutoshi Morioka 2006-06-21 06:10:09 UTC
2.6.17-1.2138_FC5 shows same problem.

Comment 5 Kazutoshi Morioka 2006-07-08 02:59:54 UTC
Today I tested this on rawhide and found that rawhide never shows this problem.
Tested kernel was 2.6.17-1.2339.fc6, 2.6.17-1.2356.fc6 and 2.6.17-1.2358.fc6PAE.
I don't know what time this was fixed.
At least, when I was filed #192924, rawhide showed same problem.

Comment 6 Kazutoshi Morioka 2006-09-25 23:58:46 UTC
Today's updates-testing for FC5, 2.6.18-1.2189.fc5 wiped out this problem.
So, I think this bug can be closed. Thank you.

Comment 7 Alasdair Kergon 2006-09-26 07:15:42 UTC
OK, thanks for letting us know.

Comment 8 David Nadle 2006-10-21 19:15:40 UTC
This may have to be reopened. I'm seeing the problem in 2.6.18-1.2200.fc5.

I have a backup script that creates four snapsnots:

lvcreate -L 512M -s -n snapXX /dev/VolGroup00/LogVolXX

Where XX is 00, 01, 02, 03.

00 and 02 always succeed. 01 and 03 always fail with the message:

LV VolGroup00/snapXX in use: not deactivating
Couldn't deactivate new snapsnot.

lvs displays the following:

  LV       VG         Attr   LSize   Origin   Snap%  Move Log Copy% 
  LogVol00 VolGroup00 owi-ao  10.00G                                
  LogVol01 VolGroup00 -wi-ao  20.00G                                
  LogVol02 VolGroup00 owi-ao  20.00G                                
  LogVol03 VolGroup00 -wi-ao  40.00G                                
  snap00   VolGroup00 swi-a- 512.00M LogVol00   3.20                
  snap01   VolGroup00 -wi-a- 512.00M                                
  snap02   VolGroup00 swi-a- 512.00M LogVol02   2.03                
  snap03   VolGroup00 -wi-a- 512.00M                                

The udevcontrol workaround described in Comment #3 does work. After wrapping my 
four lvcreate lines with the udevcontrol commands all four snapshots were 
created successfully. 

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