sched/topology: Introduce for_each_numa_hop_mask()

The recently introduced sched_numa_hop_mask() exposes cpumasks of CPUs
reachable within a given distance budget, wrap the logic for iterating over
all (distance, mask) values inside an iterator macro.
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/topology.h

@@ -261,4 +261,22 @@ sched_numa_hop_mask(unsigned int node, unsigned int hops)
 }
 #endif	/* CONFIG_NUMA */
 
+/**
+ * for_each_numa_hop_mask - iterate over cpumasks of increasing NUMA distance
+ *                          from a given node.
+ * @mask: the iteration variable.
+ * @node: the NUMA node to start the search from.
+ *
+ * Requires rcu_lock to be held.
+ *
+ * Yields cpu_online_mask for @node == NUMA_NO_NODE.
+ */
+#define for_each_numa_hop_mask(mask, node)				       \
+	for (unsigned int __hops = 0;					       \
+	     mask = (node != NUMA_NO_NODE || __hops) ?			       \
+		     sched_numa_hop_mask(node, __hops) :		       \
+		     cpu_online_mask,					       \
+	     !IS_ERR_OR_NULL(mask);					       \
+	     __hops++)
+
 #endif /* _LINUX_TOPOLOGY_H */