linux-kernel - Re: [PATCH] x86/numa: Use cpumask_available instead of hardcoded NULL check

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Date:   Wed, 03 Aug 2022 14:28:04 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     "Ingo Molnar" <mingo@...nel.org>
Cc:     "x86" <x86@...nel.org>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        "linux-kernel-mentees" 
        <linux-kernel-mentees@...ts.linuxfoundation.org>
Subject: Re: [PATCH] x86/numa: Use cpumask_available instead of hardcoded
 NULL check

On Wed, 03 Aug 2022 14:18:18 +0530  Ingo Molnar <mingo@...nel.org> wrote:
> 
> * Siddh Raman Pant <code@...dh.me> wrote:
> 
> > On Tue, 02 Aug 2022 16:37:44 +0530  Ingo Molnar <mingo@...nel.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
> 

There is no reason why allmodconfig would trigger the warning, as it has
CONFIG_CPUMASK_OFFSTACK=y, but the warning is because of the other case.
Still, I tried that, and as expected there was no warning.

Did you try the config file I had linked to earlier?

Thanks,
Siddh