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

[Peter Zijlstra]

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.