Re: FS hang when creating snapshots on a UFS SU+J setup

Bryce Edwards <bryce <at> bryce.net> writes:

> 
> I have a RELENG_9 machine that hangs when a snapshot is created on the
> root fs (UFS, with SU+J).  More accurately, all the processes show a
> state of "suspfs" (with ^T) and no fs activity is completed from then
> on.  A hard reboot (power cycle) was the only way to proceed.
> 
> Here's some reference info - let me know what else I should provide.
> 
> $uname -a
> FreeBSD xxx.xxx.net 9.0-PRERELEASE FreeBSD 9.0-PRERELEASE #0: Sun Dec
> 25 05:04:37 UTC 2011     root <at> xxx.xxx.net:/usr/obj/usr/src/sys/GENERIC
> amd64
> 
> csup was run just before build[world|kernel] so you have reference on
> the version information.
> 
> $mount
> /dev/gpt/root on / (ufs, local, journaled soft-updates)
> devfs on /dev (devfs, local, multilabel)
> linprocfs on /compat/linux/proc (linprocfs, local)
> { zfs info removed }
> 
> $df -h
> Filesystem                  Size    Used   Avail Capacity  Mounted on
> /dev/gpt/root               454G    9.1G    409G     2%    /
> devfs                       1.0k    1.0k      0B   100%    /dev
> linprocfs                   4.0k    4.0k      0B   100%    /compat/linux/proc
> { zfs info removed }
> 
> After the hard reset, there was a snapshot file listed in /.snap and
> it was ~465 GB, iirc.  Unfortunately, I needed to get things going
> again so I was not able to debug or diagnose further.  I may be able
> to schedule a time that I could recreate the issue and diagnose
> better, but I wanted to get your input on what data points and/or
> command you would be interested in.
> 
> Thanks in advance,
> 
> Bryce
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> 


Hi,

May be i overlooked something but i can confirm the two precedents reports
and PR kern/163310, i have the same freeze when trying to issue snapshot on the 
root fs when SUJ is ON.

With 9-PRERELEASE and 10-CURRENT 

There was an old closed PR (may be or not) related to this PB:

http://www.freebsd.org/cgi/query-pr.cgi?pr=160662

I never be able to create a snapshot when SUJ is activated.

I use the STOCK GENERIC KERNEL ( System build form OFFICIAL RC ISO or from make 
world / no special make.conf)

This PB occurs on several hardware and also in VM under VBox4 

After the freeze i need to halt the system by pressing 5 seconds the power 
switch.
Sometimes, the SUJ recovery is not enough, i have a PANIC with DUP ALLOC
when i issue a full fsck -yf in single user, i got some files reconnected in 
lost+found and some rare recovery messages.

To reproduce:

Prior doing snapshot, i have fully checked with FSCK the integrity of the fs in 
single user mode.

And just issue : mksnap_ffs /.snap/backup
( dump -L may also suffer from this )

My setup: ( NO ZFS / 4 GB / CORE 2 DUO / SATA 7.2k in ahci mode) 

FreeBSD test.test.test 9.0-PRERELEASE FreeBSD 9.0-PRERELEASE #0: Sun Jan  1 
13:35:33 CET 2012     root_at_test.test.test:/usr/obj/usr/src/sys/GENERIC  amd64

/dev/ufs/ROOTFS on / (ufs, local, journaled soft-updates)
devfs on /dev (devfs, local, multilabel)
fdescfs on /dev/fd (fdescfs)
procfs on /proc (procfs, local)

Notice that nearly no fs activity occurring while doing this snapshot.

Also no problems when SUJ is disable.

Anyway, thanks so much for your wonderful and heavy work.

It will be great to merge SUJ on 8.3 RELEASE when things got stable.

Best wishes of happiness and success for this new year !

Alain from Paris.
In love with FreeBSD since 386BSD 0.1 :-)