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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Wed, 3 Aug 2022 10:48:18 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Siddh Raman Pant <code@siddh.me>
Cc:     x86 <x86@kernel.org>, Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-kernel-mentees 
        <linux-kernel-mentees@lists.linuxfoundation.org>
Subject: Re: [PATCH] x86/numa: Use cpumask_available instead of hardcoded
 NULL check
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* Siddh Raman Pant <code@siddh.me> wrote:

> On Tue, 02 Aug 2022 16:37:44 +0530  Ingo Molnar <mingo@kernel.org> wrote:
> > Your fix makes sense I suppose, but I'm wondering how testing didn't 
> > trigger this warning.
> > 
> > Off-stack isn't a rare config option:
> > 
> >   kepler:~/tip> make allmodconfig
> >   #
> >   # No change to .config
> >   #
> >   kepler:~/tip> grep CPUMASK_OFFSTACK .config
> >   CONFIG_CPUMASK_OFFSTACK=y
> >   kepler:~/tip> 
> > 
> > What am I missing?
> 
> Maybe this triggers on certain config options set, or maybe due to new
> gcc version? (I'm using gcc-12, I also likely saw while on gcc-11.)
> It nevertheless is a helpful warning.
> 
> I just now tried `make defconfig` (default configuration based on
> 'x86_64_defconfig') and compiling with `make -j13 all`, and gcc doesn't
> give any warning. (CONFIG_CPUMASK_OFFSTACK isn't even listed in the
> .config file produced, grep fails.)

Does 'allmodconfig' reproduce the warning for you:

  $ make allmodconfig
  $ make arch/x86/mm/numa.o

?

If yes, then this could be due to gcc-12, as it doesn't reproduce with 
gcc-11 for me:

   gcc version 11.2.0 (Ubuntu 11.2.0-19ubuntu1) 

Thanks,

	Ingo