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

From: Ingo Molnar <mingo@kernel.org>
To: Siddh Raman Pant <code@siddh.me>
Cc: 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
Date: Tue, 2 Aug 2022 13:07:44 +0200	[thread overview]
Message-ID: <YukFgFTaq4Aw+uht@gmail.com> (raw)
In-Reply-To: <20220731160913.632092-1-code@siddh.me>

* Siddh Raman Pant <code@siddh.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