sched/topology: Handle NUMA_NO_NODE in sched_numa_find_nth_cpu()

sched_numa_find_nth_cpu() doesn't handle NUMA_NO_NODE properly, and
may crash kernel if passed with it. On the other hand, the only user
of sched_numa_find_nth_cpu() has to check NUMA_NO_NODE case explicitly.

It would be easier for users if this logic will get moved into
sched_numa_find_nth_cpu().

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Link: https://lore.kernel.org/r/20230819141239.287290-6-yury.norov@gmail.com

kernel/sched/topology.c

@@ -2126,6 +2126,9 @@ int sched_numa_find_nth_cpu(const struct cpumask *cpus, int cpu, int node)
 	struct cpumask ***hop_masks;
 	int hop, ret = nr_cpu_ids;
 
+	if (node == NUMA_NO_NODE)
+		return cpumask_nth_and(cpu, cpus, cpu_online_mask);
+
 	rcu_read_lock();
 
 	/* CPU-less node entries are uninitialized in sched_domains_numa_masks */

lib/cpumask.c

@@ -146,9 +146,7 @@ unsigned int cpumask_local_spread(unsigned int i, int node)
 	/* Wrap: we always want a cpu. */
 	i %= num_online_cpus();
 
-	cpu = (node == NUMA_NO_NODE) ?
-		cpumask_nth(i, cpu_online_mask) :
-		sched_numa_find_nth_cpu(cpu_online_mask, i, node);
+	cpu = sched_numa_find_nth_cpu(cpu_online_mask, i, node);
 
 	WARN_ON(cpu >= nr_cpu_ids);
 	return cpu;