linux-hardening - [PATCH 2/3] printk: kunit: support offstack cpumask

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Message-ID: <20250702095157.110916-3-pmladek@suse.com>
Date: Wed,  2 Jul 2025 11:51:56 +0200
From: Petr Mladek <pmladek@...e.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
	John Ogness <john.ogness@...utronix.de>,
	Dan Carpenter <dan.carpenter@...aro.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Kees Cook <kees@...nel.org>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	David Gow <davidgow@...gle.com>,
	Arnd Bergmann <arnd@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Petr Mladek <pmladek@...e.com>
Subject: [PATCH 2/3] printk: kunit: support offstack cpumask

From: Arnd Bergmann <arnd@...db.de>

For large values of CONFIG_NR_CPUS, the newly added kunit test fails
to build:

kernel/printk/printk_ringbuffer_kunit_test.c: In function 'test_readerwriter':
kernel/printk/printk_ringbuffer_kunit_test.c:279:1: error: the frame size of 1432 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]

Change this to use cpumask_var_t and allocate it dynamically when
CONFIG_CPUMASK_OFFSTACK is set.

Fixes: 5ea2bcdfbf46 ("printk: ringbuffer: Add KUnit test")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
[pmladek@...e.com: Correctly handle allocation failures and freeing using KUnit test API.]
Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 kernel/printk/printk_ringbuffer_kunit_test.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/kernel/printk/printk_ringbuffer_kunit_test.c b/kernel/printk/printk_ringbuffer_kunit_test.c
index 217dcc14670c..0c3030fde8c2 100644
--- a/kernel/printk/printk_ringbuffer_kunit_test.c
+++ b/kernel/printk/printk_ringbuffer_kunit_test.c
@@ -216,6 +216,7 @@ static int prbtest_reader(struct prbtest_data *test_data, unsigned long timeout_
 	return 0;
 }
 
+KUNIT_DEFINE_ACTION_WRAPPER(prbtest_cpumask_cleanup, free_cpumask_var, cpumask_var_t);
 KUNIT_DEFINE_ACTION_WRAPPER(prbtest_kthread_cleanup, kthread_stop, struct task_struct *);
 
 static void prbtest_add_kthread_cleanup(struct kunit *test, struct task_struct *kthread)
@@ -240,8 +241,13 @@ static void test_readerwriter(struct kunit *test)
 	struct prbtest_thread_data *thread_data;
 	struct prbtest_data *test_data;
 	struct task_struct *thread;
-	cpumask_t test_cpus;
+	cpumask_var_t test_cpus;
 	int cpu, reader_cpu;
+	int err;
+
+	KUNIT_ASSERT_TRUE(test, alloc_cpumask_var(&test_cpus, GFP_KERNEL));
+	err = kunit_add_action_or_reset(test, prbtest_cpumask_cleanup, test_cpus);
+	KUNIT_ASSERT_EQ(test, err, 0);
 
 	cpus_read_lock();
 	/*
@@ -250,15 +256,15 @@ static void test_readerwriter(struct kunit *test)
 	 * Instead use a snapshot of the online CPUs.
 	 * If they change during test execution it is unfortunate but not a grave error.
 	 */
-	cpumask_copy(&test_cpus, cpu_online_mask);
+	cpumask_copy(test_cpus, cpu_online_mask);
 	cpus_read_unlock();
 
 	/* One CPU is for the reader, all others are writers */
-	reader_cpu = cpumask_first(&test_cpus);
-	if (cpumask_weight(&test_cpus) == 1)
+	reader_cpu = cpumask_first(test_cpus);
+	if (cpumask_weight(test_cpus) == 1)
 		kunit_warn(test, "more than one CPU is recommended");
 	else
-		cpumask_clear_cpu(reader_cpu, &test_cpus);
+		cpumask_clear_cpu(reader_cpu, test_cpus);
 
 	/* KUnit test can get restarted more times. */
 	prbtest_prb_reinit(&test_rb);
@@ -271,7 +277,7 @@ static void test_readerwriter(struct kunit *test)
 
 	kunit_info(test, "running for %lu ms\n", runtime_ms);
 
-	for_each_cpu(cpu, &test_cpus) {
+	for_each_cpu(cpu, test_cpus) {
 		thread_data = kunit_kmalloc(test, sizeof(*thread_data), GFP_KERNEL);
 		KUNIT_ASSERT_NOT_NULL(test, thread_data);
 		thread_data->test_data = test_data;
-- 
2.50.0