Re: [PATCH 1/2] sched: topology: Fix topology validation error

[Peter Zijlstra]

On Fri, Aug 22, 2025 at 01:14:14PM -0700, Tim Chen wrote:
> From: Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>
> 
> As sd_numa_mask() (the function behind tl->mask() for the NUMA levels
> of the topology) depends on the value of sched_domains_curr_level,
> it's possible to be iterating over a level while, sd_numa_mask()
> thinks we are in another, causing the topology validation to fail (for
> valid cases).
> 
> Set sched_domains_curr_level to the current topology level while
> iterating.
> 
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>
> Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> ---
>  kernel/sched/topology.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 977e133bb8a4..9a7ac67e3d63 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -2394,6 +2394,14 @@ static bool topology_span_sane(const struct cpumask *cpu_map)
>  	for_each_sd_topology(tl) {
>  		int tl_common_flags = 0;
>  
> +#ifdef CONFIG_NUMA
> +		/*
> +		 * sd_numa_mask() (one of the possible values of
> +		 * tl->mask()) depends on the current level to work
> +		 * correctly.
> +		 */

This is propagating that ugly hack from sd_init(), isn't it. Except its
pretending like its sane code... And for what?

> +		sched_domains_curr_level = tl->numa_level;
> +#endif
>  		if (tl->sd_flags)
>  			tl_common_flags = (*tl->sd_flags)();
>  
		if (tl_common_flags & SD_NUMA)
			continue;

So how does this make any difference ?

We should never get to calling tl->mask() for NUMA.