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SubjectRe: Kunit test failures with cpumask tests on parisc
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On 2/5/24 07:53, Guenter Roeck wrote:
> when running cpumask Kunit tests on parisc/parisc64 in qemu,
> I get the following errors.
>
> KTAP version 1
> # Subtest: cpumask
> # module: cpumask_kunit
> 1..6
> # test_cpumask_weight: EXPECTATION FAILED at lib/cpumask_kunit.c:68
> Expected nr_cpu_ids == cpumask_weight(((const struct cpumask *)&__cpu_possible_mask)), but
> nr_cpu_ids == 16 (0x10)
> cpumask_weight(((const struct cpumask *)&__cpu_possible_mask)) == 1 (0x1)
> cpu_possible_mask contains CPUs 0
> not ok 1 test_cpumask_weight
> # test_cpumask_first: EXPECTATION FAILED at lib/cpumask_kunit.c:79
> Expected nr_cpu_ids <= cpumask_first_zero(((const struct cpumask *)&__cpu_possible_mask)), but
> nr_cpu_ids == 16 (0x10)
> cpumask_first_zero(((const struct cpumask *)&__cpu_possible_mask)) == 1 (0x1)
> cpu_possible_mask contains CPUs 0
> not ok 2 test_cpumask_first
> # test_cpumask_last: EXPECTATION FAILED at lib/cpumask_kunit.c:87
> Expected nr_cpu_ids - 1 == cpumask_last(((const struct cpumask *)&__cpu_possible_mask)), but
> nr_cpu_ids - 1 == 15 (0xf)
> cpumask_last(((const struct cpumask *)&__cpu_possible_mask)) == 0 (0x0)
> cpu_possible_mask contains CPUs 0
> not ok 3 test_cpumask_last
> # test_cpumask_next: EXPECTATION FAILED at lib/cpumask_kunit.c:94
> Expected nr_cpu_ids <= cpumask_next_zero(-1, ((const struct cpumask *)&__cpu_possible_mask)), but
> nr_cpu_ids == 16 (0x10)
> cpumask_next_zero(-1, ((const struct cpumask *)&__cpu_possible_mask)) == 1 (0x1)
> cpu_possible_mask contains CPUs 0
> not ok 4 test_cpumask_next
> ok 5 test_cpumask_iterators
> ok 6 test_cpumask_iterators_builtin
> # cpumask: pass:2 fail:4 skip:0 total:6
> # Totals: pass:2 fail:4 skip:0 total:6
> not ok 5 cpumask
>
> It appears that parisc sets __cpu_possible_mask to the number of online CPUs,
> which is limited in qemu and doesn't match CONFIG_NR_CPUS. Is this a problem
> with the unit test or with the parisc architecture, or does the unit test
> simply not apply for parisc ?

Thank you for finding and reporting this!
It's a bug (or a misunderstanding) in the parisc kernel.
Reverting commit 0921244f6f4f ("parisc: Only list existing CPUs in cpu_possible_mask")
fixes the KUnit test.

Furthermore the revert fixes the issue that CPU hot-unplugging doesn't
work and which I just was starting to debug:
https://lore.kernel.org/lkml/Zb0mbHlIud_bqftx@slm.duckdns.org/t/

Helge

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