threads/136345: Recursive read rwlocks in thread A cause deadlock with write lock in thread B

Attilio Rao attilio at
Thu Jul 16 12:48:13 UTC 2009

2009/7/16 Attilio Rao <attilio at>:
> 2009/7/15 Nick Esborn <nick at>:
>> The following reply was made to PR threads/136345; it has been noted by GNATS.
>> From: Nick Esborn <nick at>
>> To: bug-followup at,
>>  rink at
>> Cc:
>> Subject: Re: threads/136345: Recursive read rwlocks in thread A cause deadlock with write lock in thread B
>> Date: Wed, 15 Jul 2009 14:32:38 -0700
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>>  Even after the above patch, I still run into occasional MySQL thread
>>  deadlocks, which I originally described in what is now threads/135673.
>>  I also posted on freebsd-current a few days ago:
>>  I'd be happy to collect whatever data would be helpful in tracking
>>  down this deadlock.  This only seems to happen under our production
>>  workload, so that might make it harder to capture meaningful debug
>>  data, but I'm certainly willing to try.  I can also arrange for
>>  developer access to the system in question, if that would help
>>  significantly.
> So did you backport this to 7 and still experience deadlocks?
> I just committed the fix to HEAD not to STABLE branch.

Ok, I got, you just upgraded.
Can you try the following things?:
- Upgrade to the -CURRENT of today
- Recompile the kernel with the following options:
- When the deadlock takes place break into DDB and please retrieve the
following info:
db> show allpcpu
db> ps
db> alltrace
db> show alllock

- Save them with a serial console output or using the textdump(4) format.

(if necessary read the ddb(4) and textdump(4) before to set up the
whole system).
This would shade a light if the problem lives within the kernel or not.


Peace can only be achieved by understanding - A. Einstein

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