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

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Message-ID: <20250702202835.GA593751@ax162>
Date: Wed, 2 Jul 2025 13:28:35 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Petr Mladek <pmladek@...e.com>
Cc: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
	John Ogness <john.ogness@...utronix.de>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	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
Subject: Re: [PATCH 2/3] printk: kunit: support offstack cpumask

On Wed, Jul 02, 2025 at 11:51:56AM +0200, Petr Mladek wrote:
> 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);

This appears to break the build for me when CONFIG_CPUMASK_OFFSTACK is not
set, like when enabling this test on top of x86_64 defconfig:

  In file included from kernel/printk/printk_ringbuffer_kunit_test.c:14:
  kernel/printk/printk_ringbuffer_kunit_test.c: In function 'prbtest_cpumask_cleanup':
  include/kunit/resource.h:409:32: error: cast specifies array type
    409 |                 arg_type arg = (arg_type)in;                    \
        |                                ^
  kernel/printk/printk_ringbuffer_kunit_test.c:226:1: note: in expansion of macro 'KUNIT_DEFINE_ACTION_WRAPPER'
    226 | KUNIT_DEFINE_ACTION_WRAPPER(prbtest_cpumask_cleanup, free_cpumask_var, cpumask_var_t);
        | ^~~~~~~~~~~~~~~~~~~~~~~~~~~

Clang's error might be a little clearer with the "aka" note it provides.

  kernel/printk/printk_ringbuffer_kunit_test.c:226:1: error: used type 'cpumask_var_t' (aka 'struct cpumask[1]') where arithmetic or pointer type is required
    226 | KUNIT_DEFINE_ACTION_WRAPPER(prbtest_cpumask_cleanup, free_cpumask_var, cpumask_var_t);
        | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  include/kunit/resource.h:409:18: note: expanded from macro 'KUNIT_DEFINE_ACTION_WRAPPER'
    409 |                 arg_type arg = (arg_type)in;                    \
        |                                ^         ~~

>  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
>