linux-kernel - Re: [PATCH v2 1/5] lib/test_cpumask: drop cpu_possible

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Date:   Sat, 20 Aug 2022 14:35:28 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Sander Vanheule <sander@...nheule.net>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        David Gow <davidgow@...gle.com>,
        linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
        Maíra Canal <mairacanal@...eup.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] lib/test_cpumask: drop cpu_possible_mask full test

On Sat, Aug 20, 2022 at 05:03:09PM +0200, Sander Vanheule wrote:
> When the number of CPUs that can possibly be brought online is known at
> boot time, e.g. when HOTPLUG is disabled, nr_cpu_ids may be smaller than
> NR_CPUS. In that case, cpu_possible_mask would not be completely filled,
> and cpumask_full(cpu_possible_mask) can return false for valid system
> configurations.

It doesn't mean we can just give up. You can check validity of possible
cpumask like this: 
        KUNIT_EXPECT_EQ(test, nr_cpu_ids, cpumask_first_zero(&mask_all))
        KUNIT_EXPECT_EQ(test, NR_CPUS, cpumask_first(&mask_all))
 
> Fixes: c41e8866c28c ("lib/test: introduce cpumask KUnit test suite")
> Link: https://lore.kernel.org/lkml/346cb279-8e75-24b0-7d12-9803f2b41c73@riseup.net/
> Reported-by: Maíra Canal <mairacanal@...eup.net>
> Signed-off-by: Sander Vanheule <sander@...nheule.net>
> Tested-by: Maíra Canal <mairacanal@...eup.net>
> Reviewed-by: David Gow <davidgow@...gle.com>
> ---
> Changes in v2:
> Rewrite commit message to explain why this test is wrong
> 
>  lib/test_cpumask.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/lib/test_cpumask.c b/lib/test_cpumask.c
> index a31a1622f1f6..4ebf9f5805f3 100644
> --- a/lib/test_cpumask.c
> +++ b/lib/test_cpumask.c
> @@ -54,7 +54,6 @@ static cpumask_t mask_all;
>  static void test_cpumask_weight(struct kunit *test)
>  {
>  	KUNIT_EXPECT_TRUE(test, cpumask_empty(&mask_empty));
> -	KUNIT_EXPECT_TRUE(test, cpumask_full(cpu_possible_mask));
>  	KUNIT_EXPECT_TRUE(test, cpumask_full(&mask_all));
>  
>  	KUNIT_EXPECT_EQ(test, 0, cpumask_weight(&mask_empty));
> -- 
> 2.37.2