netdev - Re: [PATCH 0/4] net: drop netif_attrmask

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Message-ID: <YzsluT4ET0zyjCtp@yury-laptop>
Date:   Mon, 3 Oct 2022 11:11:05 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Menglong Dong <imagedong@...cent.com>,
        Kuniyuki Iwashima <kuniyu@...zon.com>,
        Petr Machata <petrm@...dia.com>
Subject: Re: [PATCH 0/4] net: drop netif_attrmask_next*()

On Mon, Oct 03, 2022 at 09:50:48AM -0700, Jakub Kicinski wrote:
> On Sun,  2 Oct 2022 08:16:58 -0700 Yury Norov wrote:
> > netif_attrmask_next_and() generates warnings if CONFIG_DEBUG_PER_CPU_MAPS
> > is enabled.
> 
> Could you describe the nature of the warning? Is it a false positive 
> or a legit warning?
> 
> If the former perhaps we should defer until after the next merge window.

The problem is that netif_attrmask_next_and() is called with
n == nr_cpu_ids-1, which triggers cpu_max_bits_warn() after this:

https://lore.kernel.org/netdev/20220926103437.322f3c6c@kernel.org/

Underlying bitmap layer handles this correctly, so this wouldn't make
problems for people. But this is not a false-positive.

Thanks,
Yury