Re: [PATCH bpf-next v3 1/2] bpf: Require a BPF cpumask for bpf_cpumask_populate()

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

On Thu Jul 9, 2026 at 8:39 PM CEST, sashiko-bot wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Low] The BPF selftests and their headers were not updated to reflect the new `struct bpf_cpumask *` signature for `bpf_cpumask_populate()`.
> --
>
> --- Patch [1]: [PATCH bpf-next v3 1/2] bpf: Require a BPF cpumask for bpf_cpumask_populate() ---
> commit 79080c077263fb184f42fe92f3d8db1f3967a4b5
> Author: Nicholas Dudar <main.kalliope@gmail.com>
>
> bpf: Require a BPF cpumask for bpf_cpumask_populate()
>
> This commit changes the first argument of bpf_cpumask_populate() to require
> a struct bpf_cpumask pointer instead of a struct cpumask pointer. This
> ensures the function follows the same ownership rules as other mutating
> cpumask kfuncs.
>
>> diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
>> index b8c805b4b06a0..1336a4efa7553 100644
>> --- a/kernel/bpf/cpumask.c
>> +++ b/kernel/bpf/cpumask.c
> [ ... ]
>> @@ -467,7 +467,7 @@ __bpf_kfunc int bpf_cpumask_populate(struct cpumask *cpumask, void *src, size_t
>>  		!IS_ALIGNED(source, sizeof(long)))
>>  		return -EINVAL;
>>
>> -	bitmap_copy(cpumask_bits(cpumask), src, nr_cpu_ids);
>> +	bitmap_copy(cpumask_bits(&cpumask->cpumask), src, nr_cpu_ids);
>>
>>  	return 0;
>>  }
>> diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
>> index 87f15f2962348..3f74d522f7e79 100644
>> --- a/tools/sched_ext/include/scx/compat.bpf.h
>> +++ b/tools/sched_ext/include/scx/compat.bpf.h
>> @@ -84,7 +84,7 @@ bool scx_bpf_dispatch_vtime_from_dsq___old(struct bpf_iter_scx_dsq *it__iter, st
>>   *
>>   * Compat macro will be dropped on v6.19 release.
>>   */
>> -int bpf_cpumask_populate(struct cpumask *dst, void *src, size_t src__sz) __ksym __weak;
>> +int bpf_cpumask_populate(struct bpf_cpumask *dst, void *src, size_t src__sz) __ksym __weak;
>
> [Severity: Low]
> This isn't a bug, but should the BPF selftest headers also be updated to
> reflect this new signature?
>
> Looking at tools/testing/selftests/bpf/progs/cpumask_common.h, it appears it
> still declares the old signature for the kfunc:
>
> int bpf_cpumask_populate(struct cpumask *cpumask, void *src, size_t src__sz) __ksym __weak;
>
> Because of this, the tests in cpumask_success.c and cpumask_failure.c under
> tools/testing/selftests/bpf/progs/ continue to use explicit C-level casts
> from struct bpf_cpumask * to struct cpumask *. For example, in
> test_populate_success():
>
> ret = bpf_cpumask_populate((struct cpumask *)mask, bits, CPUMASK_TEST_MASKLEN);
>
> While this doesn't cause runtime failures since the BPF verifier matches the
> runtime register BTF type instead of C-level casts, updating the selftests
> would ensure complete consistency with the new kfunc signature.

Once this lands, please send a follow up to address this.