Re: lvcreate hangs forever during snapshot creation when suspending volume

Hi,

Zdenek Kabelac wrote:
> Now - you suggests you are able to reproduce this issue also on your bare 
> metal hw - in this case run these 3 commands  before  'lvcreate'

Here we go:

> $ dmsetup table
> devDataStore1-volMachines: 0 5368709120 linear 9:127 2048
> devDataStore2-volData: 0 11596414976 linear 259:6 2048
> devSystem-volRoot: 0 419430400 linear 8:3 50333696
> devSystem-volSwap: 0 50331648 linear 8:3 2048

> $ dmsetup info -c
> Name                      Maj Min Stat Open Targ Event  UUID
> devDataStore1-volMachines 253   1 L--w    1    1      0
LVM-AzPWjYw7Nts8ZnQyaKdjJ8cyaG0b9umSFIx2fo4zZvW8QplyYM3jNaQSFXSDMNDW
> devDataStore2-volData     253   0 L--w    1    1      0
LVM-RZtslsKN16YTBhJZE4qzFkvFQVChUKEcyUS1BwtKv3CeDUnKkTz53p8IwT5pqMnk
> devSystem-volRoot         253   3 L--w    1    1      0
LVM-TZlj0Mwy3bA5QpPVVpeO6ncufQ2Va36MgxgnvVn7fNGMme2prgc1xn9e25vua36d
> devSystem-volSwap         253   2 L--w    2    1      0
LVM-TZlj0Mwy3bA5QpPVVpeO6ncufQ2Va36Mp6kfZF6l8ubeUOo00BrK7kFGK8JvcG6X

> $ dmsetup ls --tree
> devDataStore1-volMachines (253:1)
>  L- (9:127)
> devDataStore2-volData (253:0)
>  L- (259:6)
> devSystem-volRoot (253:3)
>  L- (8:3)
> devSystem-volSwap (253:2)
>  L- (8:3)

...and during lvcreate when the system hangs:

> $ dmsetup table
> devDataStore1-volMachines: 0 5368709120 linear 9:127 2048
> devDataStore1-volMachines-real:
> devDataStore1-volMachines_snap:
> devDataStore1-volMachines_snap-cow: 0 209715200 linear 9:127 5368711168
> devDataStore2-volData: 0 11596414976 linear 259:6 2048
> devSystem-volRoot: 0 419430400 linear 8:3 50333696
> devSystem-volSwap: 0 50331648 linear 8:3 2048

> $ dmsetup info -c
> Name                               Maj Min Stat Open Targ Event  UUID
> devDataStore1-volMachines          253   1 LI-w    1    1      0
LVM-AzPWjYw7Nts8ZnQyaKdjJ8cyaG0b9umSFIx2fo4zZvW8QplyYM3jNaQSFXSDMNDW
> devDataStore1-volMachines-real     253   4 -I-w    2    0      0
LVM-AzPWjYw7Nts8ZnQyaKdjJ8cyaG0b9umSFIx2fo4zZvW8QplyYM3jNaQSFXSDMNDW-real
> devDataStore1-volMachines_snap     253   6 -I-w    0    0      0
LVM-AzPWjYw7Nts8ZnQyaKdjJ8cyaG0b9umSHue1IrGu69toKQ0ZdcbSv97i3xq5YP2v
> devDataStore1-volMachines_snap-cow 253   5 L--w    1    1      0
LVM-AzPWjYw7Nts8ZnQyaKdjJ8cyaG0b9umSHue1IrGu69toKQ0ZdcbSv97i3xq5YP2v-cow
> devDataStore2-volData              253   0 L--w    1    1      0
LVM-RZtslsKN16YTBhJZE4qzFkvFQVChUKEcyUS1BwtKv3CeDUnKkTz53p8IwT5pqMnk
> devSystem-volRoot                  253   3 L--w    1    1      0
LVM-TZlj0Mwy3bA5QpPVVpeO6ncufQ2Va36MgxgnvVn7fNGMme2prgc1xn9e25vua36d
> devSystem-volSwap                  253   2 L--w    2    1      0
LVM-TZlj0Mwy3bA5QpPVVpeO6ncufQ2Va36Mp6kfZF6l8ubeUOo00BrK7kFGK8JvcG6X

> $ dmsetup ls --tree
> devDataStore1-volMachines (253:1)
>  L- (9:127)
> devDataStore1-volMachines-real (253:4)
> devDataStore1-volMachines_snap (253:6)
> devDataStore1-volMachines_snap-cow (253:5)
>  L- (9:127)
> devDataStore2-volData (253:0)
>  L- (259:6)
> devSystem-volRoot (253:3)
>  L- (8:3)
> devSystem-volSwap (253:2)
>  L- (8:3)

> $ cat /proc/meminfo | grep Dirty
> Dirty:                0 kB

In case someone will ask: During I/O, the value increased/decreased
as expected.


Zdenek Kabelac wrote:
> Note: you could always 'experiment' without lvm2 in the picture -
> you can ran   'fsfreeze --freeze|--unfreeze'  yourself - to see whether
even 
> this command is able to finish  ?

fsfreeze caused the same problem :/

I also changed filesystem from xfs to ext4 just in case... same issue.

For testing I stopped the MDRAID and removed one NVMe disk which I
cleared and where I created a new ext4 partition. Running

  $ fsfreeze --freeze /mnt/test

returned within seconds and I was unable do any I/O against /mnt/test
as expected.

I unfreezed the filesystem and started to copy ~50GB to the volume.
After waiting 5 minutes and verifying that /proc/meminfo didn't list
any 'dirty' pages, I re-run the fsfreeze command which caused the
same issue -- system hangs. :/

I will repeat the test with the other NVMe later...

So probably a kernel/driver issue or hardware problem.


-- 
Regards,
Thomas


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