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

[sashiko-bot@kernel.org]

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.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260709182800.2037938-1-main.kalliope@gmail.com?part=1