linux-kernel - Re: [PATCH V2 1/2] net: Fixup netif_attrmask_next

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Date:   Fri, 14 Oct 2022 14:38:56 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     andriy.shevchenko@...ux.intel.com, davem@...emloft.net,
        edumazet@...gle.com, pabeni@...hat.com, linux@...musvillemoes.dk,
        yury.norov@...il.com, caraitto@...gle.com, willemb@...gle.com,
        jonolson@...gle.com, amritha.nambiar@...el.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V2 1/2] net: Fixup netif_attrmask_next_and warning

On Fri, Oct 14, 2022 at 11:35 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 13 Oct 2022 23:04:58 -0400 guoren@...nel.org wrote:
> > -     for (j = -1; j = netif_attrmask_next_and(j, online_mask, mask, nr_ids),
> > -          j < nr_ids;) {
> > +     for (j = -1; j < nr_ids;
> > +          j = netif_attrmask_next_and(j, online_mask, mask, nr_ids)) {
>
> This does not look equivalent, have you tested it?
>
> nr_ids is unsigned, doesn't it mean we'll never enter the loop?
Yes, you are right. Any unsigned int would break the result.
(gdb) p (int)-1 < (int)2
$1 = 1
(gdb) p (int)-1 < (unsigned int)2
$2 = 0
(gdb) p (unsigned int)-1 < (int)2
$4 = 0

So it should be:
 -     for (j = -1; j = netif_attrmask_next_and(j, online_mask, mask, nr_ids),
 -          j < nr_ids;) {
 +     for (j = -1; j < (int)nr_ids;
 +          j = netif_attrmask_next_and(j, online_mask, mask, nr_ids)) {

Right? Of cause, nr_ids couldn't be 0xffffffff (-1).

>
> Can we instead revert 854701ba4c and take the larger rework Yury
> has posted a week ago into net-next?



-- 
Best Regards
 Guo Ren