linux-kernel - Re: [BUG] While changing the cpufreq governor, kernel hits a bug in workqueue.c

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Date:	Mon, 07 Jul 2008 16:49:24 +0530
From:	Nageswara R Sastry <rnsastry@...ux.vnet.ibm.com>
To:	Johannes Weiner <hannes@...urebad.de>
CC:	linux-kernel@...r.kernel.org, balbir@...ux.vnet.ibm.com,
	ego@...ux.vnet.ibm.com, svaidy@...ux.vnet.ibm.com,
	davej@...emonkey.org.uk
Subject: Re: [BUG] While changing the cpufreq governor, kernel hits a bug
 in workqueue.c

Nageswara R Sastry wrote:
> Hi Johannes,
>>>> =======================================================
>>>> [ INFO: possible circular locking dependency detected ]
>>>> 2.6.25.7.cpufreq_patch #2
>>>> -------------------------------------------------------
> [...]
>>> Okay, the problem is in cpufreq_conservative.c.  We
>>> cancel_delayed_work_sync() while holding the mutex, but the work itself
>>> tries to grab it and there it deadlocks; lockdep caught that right.
>>>
>>> The hunk for _ondemand is correct, but the one for _conservative is
>>> obviously wrong, sorry :/
>>>
>>> I will whip something up and get back to you.  Thanks a lot for
>>> testing!
>>
>> Could you try the attached patch instead of the one above?
>>
>> Dave, I dropped the mutex-grabbing from the conservative worker function
>> as well as I don't see a reason for it, please correct me if I'm wrong.
>>
>>     Hannes
>>
> 
> The script is running now for more than 6 hours successfully, I will 
> continue this and let you know if there are any failures.
> 
> * I am seeing the circular locking dependency with the above patch too.
> 

Seeing sysfs hang for second cpu this time while cat file 
/sys/devices/system/cpu/cpu2/cpufreq/scaling_governor

Just to summarize
1. Circular locking dependency issue and
2. sysfs hung for scaling_governor

Thanks!!
Regards
R.Nageswara Sastry


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