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

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Message-ID: <165954131875.15455.15679349125656470840.tip-bot2@tip-bot2>
Date:   Wed, 03 Aug 2022 15:41:58 -0000
From:   "tip-bot2 for Siddh Raman Pant" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Siddh Raman Pant <code@...dh.me>, Ingo Molnar <mingo@...nel.org>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/numa: Use cpumask_available instead of
 hardcoded NULL check

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     625395c4a0f4775e0fe00f616888d2e6c1ba49db
Gitweb:        https://git.kernel.org/tip/625395c4a0f4775e0fe00f616888d2e6c1ba49db
Author:        Siddh Raman Pant <code@...dh.me>
AuthorDate:    Sun, 31 Jul 2022 21:39:13 +05:30
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 03 Aug 2022 11:44:57 +02:00

x86/numa: Use cpumask_available instead of hardcoded NULL check

GCC-12 started triggering a new warning:

  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) {
        |                                       ^~

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 original code in debug_cpumask_set_cpu() and cpumask_of_node() 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 above 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.

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>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/r/20220731160913.632092-1-code@siddh.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 e8b0615..2aadb20 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);