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

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Date:   Tue, 2 Aug 2022 13:07:44 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Siddh Raman Pant <code@...dh.me>
Cc:     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


* Siddh Raman Pant <code@...dh.me> wrote:

> GCC warning log:
> ===========================================================================
> 
> arch/x86/mm/numa.c: In function ‘cpumask_of_node’:
> arch/x86/mm/numa.c:916:39: warning: the comparison will always evaluate as ‘false’ for the address of ‘node_to_cpumask_map’ will never be NULL [-Waddress]
>   916 |         if (node_to_cpumask_map[node] == NULL) {
>       |                                       ^~

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?

> Fixes: c032ef60d1aa ("cpumask: convert node_to_cpumask_map[] to cpumask_var_t")
> Fixes: de2d9445f162 ("x86: Unify node_to_cpumask_map handling between 32 and 64bit")

These are ancient commits from 2009 & 2011.

Thanks,

	Ingo