I have a DDB session open to a crashed ZFS server

[Nikolay Denev]

On Oct 16, 2012, at 9:48 PM, Dennis Glatting <dg at pki2.com> wrote:

> 
> 
> On Tue, 16 Oct 2012, Andriy Gapon wrote:
> 
>> on 16/10/2012 19:15 John Baldwin said the following:
>>> On Tuesday, October 16, 2012 11:16:37 am Dennis Glatting wrote:
>>>> On Tue, 2012-10-16 at 08:44 -0400, John Baldwin wrote:
>>>>> On Monday, October 15, 2012 12:03:39 pm Dennis Glatting wrote:
>>>>>> FreeBSD/amd64 (mc) (ttyu0)
>>>>>> 
>>>>>> login: NMI ... going to debugger
>>>>>> [ thread pid 11 tid 100003 ]
>>>>> 
>>>>> You got an NMI, not a crash.  What happens if you just continue ('c' command)
>>>>> from DDB?
>>>>> 
>>>> 
>>>> I hit the NMI button because of the "crash," which is a misword, to get
>>>> into DDB.
>>> 
>>> Ah, I would suggest "hung" or "deadlocked" next time.  It certainly seems like
>>> a deadlock since all CPUs are idle.  Some helpful commands here might be
>>> 'show sleepchain' and 'show lockchain'.
>>> 
>>> Pick a "stuck" process (like find) and run:
>>> 
>>> 'show sleepchain <pid>'
>>> 
>>> In your case though it seems both 'find' and the various 'pbzip2' threads
>>> are stuck on a condition variable, so there isn't an easy way to identify
>>> an "owner" that is supposed to awaken these threads.  It could be a case
>>> of a missed wakeup perhaps, but you'll need to get someone more familiar
>>> with ZFS to identify where these codes should be awakened normally.
>>> 
>> 
>> I would also re-iterate a suggestion that I made to Nikolay ealrier:
>> http://article.gmane.org/gmane.os.freebsd.devel.file-systems/15981
>> 
>> BTW, in that case it turned out to be a genuine deadlock in ZFS ARC handling of
>> lowmem.
>> procstat -kk -a is a great help for analyzing such situations.
>> 
> 
> Without restarting the server and from memory, I believe the ARC on this server is 32GB. The L2ARC is a 50-60GB SSD. The ZIL is a 16GB partitioned SSD but my non-ZIL systems have the same problem. Main memory is 128GB.
> 
> I can run procstat to a serial console and scarf the output. What interval would be helpful? Five seconds? Remember when the system hangs, no commands will run so the data will be pre-hang.
> 
> BTW, it takes 4-24 hours to hang under load.
> 
> Also, are you suggesting I apply the patch in the URL and run again? I have been following your other posts but the patches you posted did not cleanly apply, so I removed them from my rev.
> 
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Hi,

I'm running with the patch from here : http://thread.gmane.org/gmane.os.freebsd.devel.file-systems/16000/focus=16017
And there were no deadlocks since it's applied.
If you're hitting the same issue as I was, this should help.

Regards,
Nikolay