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Re: [PATCH] ipvs: use div_s64 for signed division

To: "Pablo Neira Ayuso" <pablo@xxxxxxxxxxxxx>, "Julian Anastasov" <ja@xxxxxx>
Subject: Re: [PATCH] ipvs: use div_s64 for signed division
Cc: "Arnd Bergmann" <arnd@xxxxxxxxxx>, "Simon Horman" <horms@xxxxxxxxxxxx>, "Jakub Kicinski" <kuba@xxxxxxxxxx>, "Paolo Abeni" <pabeni@xxxxxxxxxx>, "Jiri Wiesner" <jwiesner@xxxxxxx>, Netdev <netdev@xxxxxxxxxxxxxxx>, lvs-devel@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, coreteam@xxxxxxxxxxxxx, linux-kernel <linux-kernel@xxxxxxxxxxxxxxx>
From: "Arnd Bergmann" <arnd@xxxxxxxx>
Date: Fri, 16 Dec 2022 12:24:15 +0100
On Fri, Dec 16, 2022, at 11:10, Pablo Neira Ayuso wrote:
> Hi Julian,
>
> On Thu, Dec 15, 2022 at 09:01:59PM +0200, Julian Anastasov wrote:
>> 
>>      Hello,
>> 
>> On Thu, 15 Dec 2022, Arnd Bergmann wrote:
>> 
>> > From: Arnd Bergmann <arnd@xxxxxxxx>
>> > 
>> > do_div() is only well-behaved for positive numbers, and now warns
>> > when the first argument is a an s64:
>> > 
>> > net/netfilter/ipvs/ip_vs_est.c: In function 'ip_vs_est_calc_limits':
>> > include/asm-generic/div64.h:222:35: error: comparison of distinct pointer 
>> > types lacks a cast [-Werror]
>> >   222 |         (void)(((typeof((n)) *)0) == ((uint64_t *)0));  \
>> >       |                                   ^~
>> > net/netfilter/ipvs/ip_vs_est.c:694:17: note: in expansion of macro 'do_div'
>> >   694 |                 do_div(val, loops);
>> 
>>      net-next already contains fix for this warning
>> and changes val to u64.
>
> Arnd's patch applies fine on top of net-next, maybe he is addressing
> something else?

No, it's the same bug. I had prepared my patch before the other fix
went in, and only one of the two is needed.

FWIW, I find my version slightly more readable, but Jakub's fix
is probably more efficient, because the unsigned 64-bit division
is better optimized on 32-bit, while div_s64() goes through an
extern function.

     Arnd

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