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

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Date:   Fri, 14 Oct 2022 08:52:19 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Guo Ren <guoren@...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, 14 Oct 2022 14:38:56 +0800 Guo Ren wrote:
> > 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).

No. You can't enter the loop with -1 as the iterator either. 
Let's move on.