netdev - Re: [net-next PATCH 0/6] ipv4/fib_trie: Cleanups to prepare for introduction of key vector

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Date:	Wed, 04 Mar 2015 10:22:44 -0800
From:	Alexander Duyck <alexander.h.duyck@...hat.com>
To:	David Miller <davem@...emloft.net>
CC:	netdev@...r.kernel.org
Subject: Re: [net-next PATCH 0/6] ipv4/fib_trie: Cleanups to prepare for introduction
 of key vector

On 03/04/2015 09:53 AM, David Miller wrote:
> From: Alexander Duyck <alexander.h.duyck@...hat.com>
> Date: Wed, 04 Mar 2015 06:51:27 -0800
>
>> If bits can be 32 then idx should be an unsigned long which is 64
>> bits.
> unsigned long is 32-bit on 32-bit platforms

Right, but if unsigned long is 32 bits then usually a pointer is as 
well.  As a result we wouldn't be able to access the upper bits of a 
node with bits == 32 since the size of the tnode would be over 4 * 2^32.

The general idea is the vmalloc should fail when we attempt to allocate 
a bits == 32 tnode on a system w/ only 32b longs.  Then again I think we 
will probably cause a memory corruption on a 32b system since we are 
probably overflowing size_t on the allocation if bits ==32.  I'll have 
to take a look as I believe we are using the offsetof macro and I am not 
sure how that handles a 64b address on a 32b system.

- Alex
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