netdev - Re: [PATCH 1/2] batman-adv: Avoid u32 overflow during gateway select

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Message-ID: <55880538.1050109@meshcoding.com>
Date:	Mon, 22 Jun 2015 14:53:12 +0200
From:	Antonio Quartulli <antonio@...hcoding.com>
To:	David Miller <davem@...emloft.net>
CC:	Sven Eckelmann <sven@...fation.org>, netdev@...r.kernel.org,
	b.a.t.m.a.n@...ts.open-mesh.org, ruben@...ifunk-nrw.de,
	ruben@...-nrw.de, mareklindner@...mailbox.ch
Subject: Re: [PATCH 1/2] batman-adv: Avoid u32 overflow during gateway select

On 21/06/15 20:27, Sven Eckelmann wrote:
> On Sunday 21 June 2015 09:37:13 David Miller wrote:
>> From: Antonio Quartulli <antonio@...hcoding.com>
>> Date: Tue, 16 Jun 2015 21:06:23 +0200
>>
>>> @@ -133,7 +133,7 @@ batadv_gw_get_best_gw_node(struct batadv_priv
>>> *bat_priv)> 
>>>  	struct batadv_neigh_node *router;
>>>  	struct batadv_neigh_ifinfo *router_ifinfo;
>>>  	struct batadv_gw_node *gw_node, *curr_gw = NULL;
>>>
>>> -	uint32_t max_gw_factor = 0, tmp_gw_factor = 0;
>>> +	uint64_t max_gw_factor = 0, tmp_gw_factor = 0;
>>>
>>>  	uint32_t gw_divisor;
>>
>> Divides are performed using these variables, so if you make
>> them 64-bit the build will fail.  You have to use one of the
>> routines in include/linux/math64.h in this situation, but
>> realize that this operation is now going to be quite expensive.
> 
> Just a minor comment: The division is currently "max_gw_factor >> 18" which 
> the compiler also outputs as such (shrd + shr on i586). This is the reason why 
> it currently also works on architectures without a native 64 bit div.


Thanks for the comment David and Sven.


David you can drop this pull request.
I'll send a new one later with a modified patch that explicitly
introduces the shift.



Thanks!

-- 
Antonio Quartulli


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