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

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Message-Id: <1217f48f-a12a-4ba1-8de5-bda4b2ad6107@app.fastmail.com>
Date: Tue, 08 Jul 2025 16:48:47 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Petr Mladek" <pmladek@...e.com>, "Nathan Chancellor" <nathan@...nel.org>
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>,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/3] printk: kunit: support offstack cpumask

On Tue, Jul 8, 2025, at 16:24, Petr Mladek wrote:
> On Wed 2025-07-02 13:28:35, Nathan Chancellor wrote:
>> On Wed, Jul 02, 2025 at 11:51:56AM +0200, Petr Mladek wrote:
>
> Thanks a lot for the nice report.
>
> The problem is how cpumask_var_t is defined in include/linux/cpumask_types.h:
>
> #ifdef CONFIG_CPUMASK_OFFSTACK
> typedef struct cpumask *cpumask_var_t;
> #else
> typedef struct cpumask cpumask_var_t[1];
> #endif /* CONFIG_CPUMASK_OFFSTACK */
>
> And KUNIT_DEFINE_ACTION_WRAPPER() expect that the 3rd parameter
> is a pointer.
>
> I am going to solve this by adding a wrapper over free_cpumask_var()
> which would work with a pointer to cpumask_var_t.

I'm not familiar enough with the cleanup mechanism of kunit,
but can't you just move the mask allocation outside of
test_readerwriter()?

> + */
> +static void prbtest_free_cpumask_var(cpumask_var_t *mask)
> +{
> +	free_cpumask_var(*mask);
> +}

Or you could pass this as a cpumask_t pointer instead,
which should do the right thing without the indirection.
> 
>  	KUNIT_ASSERT_TRUE(test, alloc_cpumask_var(&test_cpus, GFP_KERNEL));
> -	err = kunit_add_action_or_reset(test, prbtest_cpumask_cleanup, test_cpus);
> +	err = kunit_add_action_or_reset(test, prbtest_cpumask_cleanup, &test_cpus);

In my original version, I did not have the
KUNIT_ASSERT_TRUE() here, which seems sufficient since this
is not what you are testing at all, and in normal systems
this would just be a stack variable.

    Arnd