netdev - Re: [PATCH][PPPOL2TP]: Fix SMP oops in pppol2tp driver

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Date:	Mon, 11 Feb 2008 23:41:18 +0000
From:	James Chapman <jchapman@...alix.com>
To:	Jarek Poplawski <jarkao2@...il.com>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH][PPPOL2TP]: Fix SMP oops in pppol2tp driver

Jarek Poplawski wrote:
> On Mon, Feb 11, 2008 at 10:19:35PM +0000, James Chapman wrote:
> ...
>> Below is example output from lockdep. The oops is reproducible when  
>> creating/deleting lots of sessions while passing data. The lock is being  
>> acquired for read and write in softirq contexts.
>>
>> Is there a better way to fix this?
>>
>> =================================
>> [ INFO: inconsistent lock state ]
>> 2.6.24-core2 #1
>> ---------------------------------
>> inconsistent {in-softirq-R} -> {softirq-on-W} usage.
>> openl2tpd/3215 [HC0[0]:SC0[0]:HE1:SE1] takes:
>>   (&tunnel->hlist_lock){---?}, at: [<f8eea157>]
>> pppol2tp_connect+0x517/0x6d0 [pppol2tp]
>> {in-softirq-R} state was registered at:
> 
> IMHO, according to this, disabling bh should be enough. And if it's
> like in this report: only read_lock is taken from softirqs, then this
> should be necessary to change only all write_locks to write_lock_bh
> (of course unless somewhere bhs are disabled already). Unless I miss
> something?!

I thought so too. I tried _bh locks first and the problem still 
occurred. Maybe I'll try it again in case I messed something up.

-- 
James Chapman
Katalix Systems Ltd
http://www.katalix.com
Catalysts for your Embedded Linux software development

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