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

Gautam Mani gautam at execve.net
Wed Jan 11 17:42:48 UTC 2012

On Wed, Jan 11, 2012 at 10:30:39AM +0100, Yamagi Burmeister wrote:
> Hello,
> I've done some tests to verify that the problem only occures when SU+J
> is used, but not SU without J. In fact, I did run the following two
> loops on different TTYs in parallel:

I also confirm this using a similar technique. The panic is only seen
with SU+J and not with just SU. 

I did a similar cp -R /root /var/tmp ; rm -rf /var/tmp/root and the
panic was trigger with dump -0L...
I got the panic (again in less than a minute of issuing the dump command)
-- I also got the "giving up on dirty" kind of message. 

I took a picture of the screen -- I am not sure if that helps!


> Since it's much more likely that the problems described above arrise
> when the the filesystem is loaded (for example by the first loop) while
> taking the snapshot this looks like some kind of race condition or
> something like that. 

Earlier I have seen this happen with dump without any high load -- or
atleast very minimum -- again with the /var because some logs were
written or cronjob was running writing to it. That didnt panic as I
indicated in my previous email -- hogged the CPU and forced a

Do let me know if I can try something further.


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