Re: [PATCH] printk: kunit: support offstack cpumask

[Petr Mladek <pmladek@suse.com>]

On Mon 2025-06-23 08:03:29, Thomas Weißschuh wrote:
> On Fri, Jun 20, 2025 at 09:25:20PM +0200, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.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@arndb.de>
> > ---
> >  kernel/printk/printk_ringbuffer_kunit_test.c | 17 +++++++++++------
> >  1 file changed, 11 insertions(+), 6 deletions(-)
> > 
> > diff --git a/kernel/printk/printk_ringbuffer_kunit_test.c b/kernel/printk/printk_ringbuffer_kunit_test.c
> > index 4081ae051d8e..9f79bc91246e 100644
> > --- a/kernel/printk/printk_ringbuffer_kunit_test.c
> > +++ b/kernel/printk/printk_ringbuffer_kunit_test.c
> > @@ -227,9 +227,12 @@ 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;
> >  
> > +	if (alloc_cpumask_var(&test_cpus, GFP_KERNEL))
> > +		return;
> 
> IMO this shouldn't fail silently and instead should do:
> 
> KUNIT_FAIL_AND_ABORT(test, "Unable to allocate cpumask");

Also we need to call kunit_add_action_or_reset() to free the mask
when the test fails (aborts) instead of the free_cpumask_var() below.

The following changes on it top of this patch worked for me:

diff --git a/kernel/printk/printk_ringbuffer_kunit_test.c b/kernel/printk/printk_ringbuffer_kunit_test.c
index 9f79bc91246e..850e5240222c 100644
--- a/kernel/printk/printk_ringbuffer_kunit_test.c
+++ b/kernel/printk/printk_ringbuffer_kunit_test.c
@@ -203,6 +203,7 @@ 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)
@@ -229,9 +230,11 @@ static void test_readerwriter(struct kunit *test)
 	struct task_struct *thread;
 	cpumask_var_t test_cpus;
 	int cpu, reader_cpu;
+	int err;
 
-	if (alloc_cpumask_var(&test_cpus, GFP_KERNEL))
-		return;
+	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();
 	/*
@@ -279,8 +282,6 @@ static void test_readerwriter(struct kunit *test)
 	prbtest_reader(test_data, runtime_ms);
 
 	kunit_info(test, "completed test\n");
-
-	free_cpumask_var(test_cpus);
 }
 
 static struct kunit_case prb_test_cases[] = {


Arnd, could you pleae send v2 with the above changes?

Best Regards,
Petr