netdev - Re: [PATCH][XFRM] Optimize policy dumping

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Message-ID: <457444E0.8060801@trash.net>
Date:	Mon, 04 Dec 2006 16:55:12 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	hadi@...erus.ca
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH][XFRM] Optimize policy dumping

jamal wrote:
> On Mon, 2006-04-12 at 09:05 -0500, jamal wrote:
> 
>>Patrick,
>>
>>Your approach is much cleaner. Let me give these a few tests then
>>I will repost later today; forget about the callback approach for now.
>>
> 
> 
> I have just applied the policy patch; havent compiled or tested (the
> setup takes me a while to put together). But by staring, I am seeing
> that you will end up with the same thing of sending a NULL or the same
> entry twice.
> 
> Consider a simple hypothetical test. You have one one entry in the 
> xfrm_policy_inexact table that matches. It happens to be the fifth out
> of 10 elements. You find it at the 5th iteration. At the sixth iteration
> you send it and last becomes null. 
> 
> All the way down, you call func with a NULL entry. You could add a check
> to make sure it only gets invoked when last is not null, but the result
> is in such a case, you will never send a 0 count element. I am sure
> there could be other tricky scenarios like this that could be
> constructed.
> 
> Thoughts.

Double sending can't happen, but you're right about potentially
sending a NULL ptr when after setting it to NULL we don't find
any other matching elements.

This patch should fix it (and is even simpler), by moving the
check for pol->type != type before sending, we make sure that
last always contains a valid element unless count == 0.

Also fixed an incorrect gcc warning about last_dir potentially
being used uninitialized.


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