Date:   Fri, 21 Oct 2022 08:39:10 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Yujie Liu <yujie.liu@...el.com>
Cc:     Yury Norov <yury.norov@...il.com>, lkp@...ts.01.org, lkp@...el.com,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        feng.tang@...el.com, ying.huang@...el.com
Subject: Re: [lib/cpumask] 6f9c07be9d: WARNING:at_include/linux/cpumask.h:#prefill_possible_map

Hi Yukie,

On Thu, Oct 20, 2022 at 7:40 PM Yujie Liu <yujie.liu@...el.com> wrote:
> On Thu, Oct 20, 2022 at 09:11:21AM -0700, Yury Norov wrote:
> > On Thu, Oct 20, 2022 at 06:05:51PM +0800, kernel test robot wrote:
> > > We noticed that below patch adds a FORCE_NR_CPUS config, and it is
> > > expected to show a warning when this config is enabled and
> > > CONFIG_NR_CPUS doesn't match the actual number of CPUs we have. But we
> > > also noticed that it not only shows a warning but could also break boot
> > > test in some cases. We are not sure if the break is actually related to
> > > this patch or not, so we send this report FYI.
> > >
> > > We noticed that a fix patch was posted at:
> > >
> > > https://lore.kernel.org/all/20221019225939.1646349-1-yury.norov@gmail.com/
> > >
> > > FORCE_NR_CPUS won't be enabled by allmodconfig or allyesconfig after
> > > applying the fix, but looks it could still be enabled by randconfig. Not
> > > sure if this is an expected behavior, but since our test robot runs many
> > > randconfig tests, this warning could still be triggered frequently and
> > > go to boot failure at last.
> > >
> > > Please kindly help to give some advice on handling this config in our
> > > testing. Thanks.
> > >
> > > Please check below report for more details:

> > Indeed, if FORCE_NR_CPUS is enabled by randconfig, it may cause at least
> > boot warning. I'm either not sure if the following alloc_pages is
> > related to the config, but anyways...
> >
> > The most logical solution would be disabling FORCE_NR_CPUS in
> > randconfig before building the kernel. We can do it in a post-script,
> > like:
> >
> > make randconfig
> > scripts/config -d FORCE_NR_CPUS
> > scripts/config -e UNFORCE_NR_CPUS
> > make
>
> This seems to need extra work to run config script for each randconfig
> build.

While randconfig is great for doing build tests, I would not use it
for boot tests, until you have some way to make sure critical options
are enabled (or disabled).  A plain randconfig kernel is almost
guaranteed to lack some driver you need.

> > Or we can create a pre-configuration file, so that randconfig would do
> > its work based on that. We already have such pre-configs for powerpc
> > and risc:
> >         arch/riscv/configs/32-bit.config
> >         arch/powerpc/configs/32-bit.config
> >         arch/powerpc/configs/64-bit.config
> >         arch/riscv/configs/64-bit.config
> >
> > Maybe it's time to create a generic config of this sort.
>
> It would be nice to have a pre-config file to ensure this config won't
> be enabled accidentally by randconfig if users are not aware of. This
> would also be consistent with common build flow so no extra steps are
> needed.

The above configs don't contain any options controlling included
drivers.
Which options would you add to it? This is very platform-specific.

> > Please let me know if that sounds sane to you. I'm not very familiar
> > to build system things, but I'll be happy to help implementing this,
> > if needed.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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