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Date:	Tue, 19 Feb 2008 14:37:38 +0000
From:	James Chapman <>
To:	Jarek Poplawski <>
CC:	David Miller <>,
Subject: Re: [PATCH][PPPOL2TP]: Fix SMP oops in pppol2tp driver

Jarek Poplawski wrote:
> On Tue, Feb 19, 2008 at 09:03:12AM +0000, James Chapman wrote:
>> David Miller wrote:
>>> From: James Chapman <>
>>> Date: Mon, 18 Feb 2008 22:09:24 +0000
>>>> Here's a new version of the patch. The patch avoids disabling irqs
>>>> and fixes the sk_dst_get() usage that DaveM mentioned. But even with
>>>> this patch, lockdep still complains if hundreds of ppp sessions are
>>>> inserted into a tunnel as rapidly as possible (lockdep trace is
>>>> below). I can stop these errors by wrapping the call to ppp_input()
>>>> in pppol2tp_recv_dequeue_skb() with local_irq_save/restore. What is
>>>> a better fix?
>>> Firstly, let's fix one thing at a time.  Leave the sk_dst_get()
>>> thing alone until we can prove that it's part of the lockdep
>>> traces.
>> In reproducing the problem, I obtained several lockdep traces that  
>> implicated sk_dst_get().
> As a matter of fact I missed just that kind information on previous
> lockdep report, so if you could send them too this should be still
> helpful.

Here you go.

Just to be clear, the initial lockdep report was with non-bh locks. 
Yesterday's report was with _bh locks and the sk_dst_get() changes. This 
(older) report is with _bh locks but without the sk_dst_get() changes.

James Chapman
Katalix Systems Ltd
Catalysts for your Embedded Linux software development

View attachment "lockdep-sk_dst.log" of type "text/plain" (205002 bytes)

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