On 25/09/22 11:05, Yury Norov wrote:
> On Fri, Sep 23, 2022 at 04:55:40PM +0100, Valentin Schneider wrote:
>> +const struct cpumask *sched_numa_hop_mask(int node, int hops)
>> +{
>> + struct cpumask ***masks = rcu_dereference(sched_domains_numa_masks);
>> +
>> + if (node == NUMA_NO_NODE && !hops)
>> + return cpu_online_mask;
>> +
>> + if (node >= nr_node_ids || hops >= sched_domains_numa_levels)
>> + return ERR_PTR(-EINVAL);
>
> This looks like a sanity check. If so, it should go before the snippet
> above, so that client code would behave consistently.
>
nr_node_ids is unsigned, so -1 >= nr_node_ids is true.
>> +
>> + if (!masks)
>> + return NULL;
>
> In (node == NUMA_NO_NODE && !hops) case you return online cpus. Here
> you return NULL just to convert it to cpu_online_mask in the caller.
> This looks inconsistent. So, together with the above comment, this
> makes me feel that you'd do it like this:
>
> const struct cpumask *sched_numa_hop_mask(int node, int hops)
> {
> struct cpumask ***masks;
>
> if (node >= nr_node_ids || hops >= sched_domains_numa_levels)
> {
> #ifdef CONFIG_SCHED_DEBUG
> pr_err(...);
> #endif
> return ERR_PTR(-EINVAL);
> }
>
> if (node == NUMA_NO_NODE && !hops)
> return cpu_online_mask; /* or NULL */
>
> masks = rcu_dereference(sched_domains_numa_masks);
> if (!masks)
> return cpu_online_mask; /* or NULL */
>
> return masks[hops][node];
> }
If we're being pedantic, sched_numa_hop_mask() shouldn't return
cpu_online_mask in those cases, but that was the least horrible
option I found to get something sensible for the NUMA_NO_NODE /
!CONFIG_NUMA case. I might be able to better handle this with your
suggestion of having a mask iterator.
