linux-kernel - Re: lockdep warning for iscsi in 2.6.33-rc6

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Date:	Fri, 12 Feb 2010 11:21:13 -0600
From:	Mike Christie <michaelc@...wisc.edu>
To:	open-iscsi@...glegroups.com
CC:	Tao Ma <tao.ma@...cle.com>, linux-kernel@...r.kernel.org
Subject: Re: lockdep warning for iscsi in 2.6.33-rc6

On 02/09/2010 06:42 PM, Tao Ma wrote:
> Hi Mike,
>
> Mike Christie wrote:
>> On 02/09/2010 12:59 AM, Tao Ma wrote:
>>> Hi Mike,
>>> I meet with a lockdep warning for iscsi in 2.6.33-rc6.
>>> the lockdep is attached.
>>>
>>
>> If the lockdep output is saying that there is a problem with the iscsi
>> host taking its mutex then the scsi host mutex, I think that might be
>> a mistake in the lockdep detection. We always take the iscsi host
>> mutex then take the scsi host mutex.
>>
>> Could it get confused if we are scanning two hosts at the same time?
>> If it is just looking at if a lock is being taken then it would look
>> like host1 has its ihost->mutex and then took its shost->mutex, but
>> then host2 could start to get scanned at the same time, and it is
>> going to take its ihost->mutex. It would then look like we are trying
>> to grab a ihost->mutex while holding a shost->mutex. However, the
>> mutexs are not global and they are different instances of the mutex
>> because each host has its own.
> If these 2 mutexes are grabed in the same order(in your description,
> ihost->mutex first and then shost->mutex), there would be no problem.

I checked the code and we are taking the locks in the proper order, but 
I did some more testing and I do not think it was detecting what I 
thought above.

I just did a login with one iscsi session and got the lockdep warning. 
So I will do some more digging into what is going on.
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