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

[Gautam Mani]

On Tue, Jan 03, 2012 at 12:55:36PM +0000, Alain BRAUNER wrote:
> 
> 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.
> 

I confirm seeing this problem on my box. 

$ uname -a
FreeBSD linbox 9.0-PRERELEASE FreeBSD 9.0-PRERELEASE #0: Fri Dec 30
19:49:47 IST 2011     root at linbox:/usr/obj/usr/src/sys/GENERIC  i386

The source was csupped from 9-STABLE after the Christmas advisories, so
it doesnt have the commits after that. This is the GENERIC kernel.

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

In my case, I am trying to take a backup using dump, and I was able to
for e.g., take a backup of /, but failed with /var. Since I use tmux, I
know that mksnap_ffs had taken over the machine -- the box was only
slightly interactive -- I could type ps axl, but did not get any output.
CPU utilisation was at 100% and the only way I could get out of it was
to hit the reset button the the box. 

> 
> Also no problems when SUJ is disable.

+1, I have switched SUJ off and now just have SU on like in 8-STABLE,
and am seeing no problems with my backups. 

Is this a known issue with SUJ -- and is SUJ not yet ready to be used on
9-STABLE?

Cheers,
Gautam

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