Re: bpf/selftests: test_access_variable_array breaks due to sched_domain::span removal

[Alan Maguire]

On 08/04/2026 08:56, Peter Zijlstra wrote:
> On Wed, Apr 08, 2026 at 10:21:46AM +0530, Saket Kumar Bhaskar wrote:
> 
>> We do have cpumask as [] array in sched_group:
>>
>> struct sched_group {
>> 	struct sched_group	*next;			/* Must be a circular list */
>> 	atomic_t		ref;
>>
>> 	unsigned int		group_weight;
>> 	unsigned int		cores;
>> 	struct sched_group_capacity *sgc;
>> 	int			asym_prefer_cpu;	/* CPU of highest priority in group */
>> 	int			flags;
>>
>> 	/*
>> 	 * The CPUs this group covers.
>> 	 *
>> 	 * NOTE: this field is variable length. (Allocated dynamically
>> 	 * by attaching extra space to the end of the structure,
>> 	 * depending on how many CPUs the kernel has booted up with)
>> 	 */
>> 	unsigned long		cpumask[];
>> };
> 
> For now. But given how utterly broken flex arrays are, this thing will
> be gone the second we run into that same thing again.
> 
>> Wouldn't be good if it is used as:
>>
>> cpumask0 = sg->cpumask[0];
> 
> I'm thinking Alexei's point is that this test should not rely on random
> kernel code.
> 

looks like we already have

struct bpf_testmod_struct_arg_3 {
        int a;
        int b[];
};

and function 

int bpf_testmod_test_struct_arg_3(int a, int b, struct bpf_testmod_struct_arg_2 c);

...in selftests/bpf/test_kmods/bpf_testmod.c so we could potentially use that instead.

Alan