linux-kernel - Re: [PATCH] ipvs: use div

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Date:   Fri, 16 Dec 2022 12:24:15 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Pablo Neira Ayuso" <pablo@...filter.org>,
        "Julian Anastasov" <ja@....bg>
Cc:     "Arnd Bergmann" <arnd@...nel.org>,
        "Simon Horman" <horms@...ge.net.au>,
        "Jakub Kicinski" <kuba@...nel.org>,
        "Paolo Abeni" <pabeni@...hat.com>,
        "Jiri Wiesner" <jwiesner@...e.de>, Netdev <netdev@...r.kernel.org>,
        lvs-devel@...r.kernel.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ipvs: use div_s64 for signed division

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@...db.de>
>> > 
>> > 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