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

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Date:   Sun, 31 Jul 2022 21:39:13 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     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>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        linux-kernel-mentees 
        <linux-kernel-mentees@...ts.linuxfoundation.org>
Subject: [PATCH] x86/numa: Use cpumask_available instead of hardcoded NULL check

node_to_cpumask_map is of type cpumask_var_t[].

When CONFIG_CPUMASK_OFFSTACK is set, cpumask_var_t is typedef'd to a
pointer for dynamic allocation, else to an array of one element. The
"wicked game" can be checked on line 700 of include/linux/cpumask.h.

The lines changed in this commit were probably written by the original
authors with CONFIG_CPUMASK_OFFSTACK=y (i.e. dynamic allocation) in mind,
checking if the cpumask was available via a direct NULL check.

When CONFIG_CPUMASK_OFFSTACK is not set, GCC gives the below given warning
while compiling the kernel.

Fix that by using cpumask_available(), which does the NULL check when
CONFIG_CPUMASK_OFFSTACK is set, otherwise returns true. Use it wherever
such checks are made.

Conditional definitions of cpumask_available() can be found along with
the definition of cpumask_var_t. Check the cpumask.h reference mentioned
above.

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) {
      |                                       ^~
In file included from ./include/linux/linkage.h:7,
                 from ./include/linux/kernel.h:17,
                 from ./arch/x86/include/asm/percpu.h:27,
                 from ./arch/x86/include/asm/current.h:6,
                 from ./include/linux/mutex.h:14,
                 from ./include/linux/kernfs.h:11,
                 from ./include/linux/sysfs.h:16,
                 from ./include/linux/kobject.h:20,
                 from ./include/linux/of.h:17,
                 from ./include/linux/irqdomain.h:35,
                 from ./include/linux/acpi.h:13,
                 from arch/x86/mm/numa.c:3:
arch/x86/mm/numa.c:67:15: note: ‘node_to_cpumask_map’ declared here
   67 | EXPORT_SYMBOL(node_to_cpumask_map);
      |               ^~~~~~~~~~~~~~~~~~~
./include/linux/export.h:87:28: note: in definition of macro ‘___EXPORT_SYMBOL’
   87 |         extern typeof(sym) sym;                                                 \
      |                            ^~~
./include/linux/export.h:147:41: note: in expansion of macro ‘__EXPORT_SYMBOL’
  147 | #define _EXPORT_SYMBOL(sym, sec)        __EXPORT_SYMBOL(sym, sec, "")
      |                                         ^~~~~~~~~~~~~~~
./include/linux/export.h:150:41: note: in expansion of macro ‘_EXPORT_SYMBOL’
  150 | #define EXPORT_SYMBOL(sym)              _EXPORT_SYMBOL(sym, "")
      |                                         ^~~~~~~~~~~~~~
arch/x86/mm/numa.c:67:1: note: in expansion of macro ‘EXPORT_SYMBOL’
   67 | EXPORT_SYMBOL(node_to_cpumask_map);
      | ^~~~~~~~~~~~~

===========================================================================

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")

Signed-off-by: Siddh Raman Pant <code@...dh.me>
---
 arch/x86/mm/numa.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index e8b061557887..2aadb2019b4f 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -867,7 +867,7 @@ void debug_cpumask_set_cpu(int cpu, int node, bool enable)
 		return;
 	}
 	mask = node_to_cpumask_map[node];
-	if (!mask) {
+	if (!cpumask_available(mask)) {
 		pr_err("node_to_cpumask_map[%i] NULL\n", node);
 		dump_stack();
 		return;
@@ -913,7 +913,7 @@ const struct cpumask *cpumask_of_node(int node)
 		dump_stack();
 		return cpu_none_mask;
 	}
-	if (node_to_cpumask_map[node] == NULL) {
+	if (!cpumask_available(node_to_cpumask_map[node])) {
 		printk(KERN_WARNING
 			"cpumask_of_node(%d): no node_to_cpumask_map!\n",
 			node);
-- 
2.35.1