linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference at 00000000000000a0

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Message-ID: <4C224E06.40806@iki.fi>
Date:	Wed, 23 Jun 2010 21:10:14 +0300
From:	Timo Teräs <timo.teras@....fi>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"Justin P.Mattock" <justinmattock@...il.com>,
	"John W.Linville" <linville@...driver.com>, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	davem@...emloft.net
Subject: Re: BUG: unable to handle kernel NULL pointer dereference at 00000000000000a0

On 06/23/2010 08:29 PM, Eric Dumazet wrote:
> Le mercredi 23 juin 2010 à 10:00 -0700, Justin P. Mattock a écrit :
>> o.k. the bisect is pointing to the below results..
>> (I tried git revert xxx but this commit is too big
>> so I'll(hopefully)manually revert it on the latest HEAD to
>> see if this is the actual problem im experiencing)
>>
>> 80c802f3073e84c956846e921e8a0b02dfa3755f is the first bad commit
>> commit 80c802f3073e84c956846e921e8a0b02dfa3755f
>> Author: Timo TerÃ¤s <timo.teras@....fi>
>> Date:   Wed Apr 7 00:30:05 2010 +0000
>>
>>      xfrm: cache bundles instead of policies for outgoing flows
>>
>>      __xfrm_lookup() is called for each packet transmitted out of
>>      system. The xfrm_find_bundle() does a linear search which can
>>      kill system performance depending on how many bundles are
>>      required per policy.
>>
>>      This modifies __xfrm_lookup() to store bundles directly in
>>      the flow cache. If we did not get a hit, we just create a new
>>      bundle instead of doing slow search. This means that we can now
>>      get multiple xfrm_dst's for same flow (on per-cpu basis).
>>
>>      Signed-off-by: Timo Teras <timo.teras@....fi>
>>      Signed-off-by: David S. Miller <davem@...emloft.net>
>>
>> :040000 040000 d8e60f5fa4c1329f450d9c7cdf98b34e6a177f22 
>> 9f576e68e5bf4ce357d7f0305aee5f410250dfe2 M      include
>> :040000 040000 f2876df688ee36907af7b4123eea96592faaed3e 
>> a3f6f6f94f0309106856cd99b38ec90b024eb016 M      net
> 
> Thanks a lot for bisecting Jutin, this is really appreciated.
> 
> crash is in xfrm_bundle_ok()
> 
> if (xdst->policy_genid != atomic_read(&xdst->pols[0]->genid))
> 	return 0;
> 
> xdst->pols[0] contains a NULL pointer

That does not really make sense, if we get this far; there's a valid
xfrm_state with the bundle. This means that there existed a policy with
it too.

I'll take a deeper look at this tomorrow. Would it be possible to see
your xfrm policies?

- Timo
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