reuseport_bpf_numa case failed when testing on a platform with CXL
memory:

    #./reuseport_bpf_numa
    ---- IPv4 UDP ----
    send node 0, receive socket 0
    ./reuseport_bpf_numa: failed to pin to node: Invalid argument

The root cause is that the platform has 2 numa nodes: node 0 has
both cpu and memory, while node 1 is a CXL node which only has
memory, and caused numa_run_on_node() to fail.

Add sanity check to skip cpuless numa node for the numa binding test.

Signed-off-by: Feng Tang <feng.tang@linux.alibaba.com>
---
Changelog:
  since v2:
    * fix spelling issue (Jakub, Sashiko)
	* remove unnecessary 'inline' for is_cpuless_node() (Jakub)

  since v1:
    * address comments from Sashiko bot
      https://lore.kernel.org/all/20260730113738.41C901F000E9@smtp.kernel.org/
    * lift the cpuless node check out of send_from_node() 

 .../selftests/net/reuseport_bpf_numa.c        | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/tools/testing/selftests/net/reuseport_bpf_numa.c b/tools/testing/selftests/net/reuseport_bpf_numa.c
index 8ec52fc5ef41..6e4817ef57c5 100644
--- a/tools/testing/selftests/net/reuseport_bpf_numa.c
+++ b/tools/testing/selftests/net/reuseport_bpf_numa.c
@@ -104,6 +104,26 @@ static void attach_bpf(int fd)
 	close(bpf_fd);
 }
 
+/*
+ * Return true if it is a cpuless node. Return false if it isn't or any
+ * error (very unlikely) happens during the libnuma calls.
+ */
+static bool is_cpuless_node(int node_id)
+{
+	struct bitmask *cpumask;
+	bool ret = false;
+
+	cpumask = numa_allocate_cpumask();
+	if (!cpumask)
+		return ret;
+
+	if (!numa_node_to_cpus(node_id, cpumask) && !numa_bitmask_weight(cpumask))
+		ret = true;
+
+	numa_bitmask_free(cpumask);
+	return ret;
+}
+
 static void send_from_node(int node_id, int family, int proto)
 {
 	struct sockaddr_storage saddr, daddr;
@@ -213,6 +233,8 @@ static void test(int *rcv_fd, int len, int family, int proto)
 	for (node = 0; node < len; ++node) {
 		if (!numa_bitmask_isbitset(numa_nodes_ptr, node))
 			continue;
+		if (is_cpuless_node(node))
+			continue;
 		send_from_node(node, family, proto);
 		receive_on_node(rcv_fd, len, epfd, node, proto);
 	}
@@ -221,6 +243,8 @@ static void test(int *rcv_fd, int len, int family, int proto)
 	for (node = len - 1; node >= 0; --node) {
 		if (!numa_bitmask_isbitset(numa_nodes_ptr, node))
 			continue;
+		if (is_cpuless_node(node))
+			continue;
 		send_from_node(node, family, proto);
 		receive_on_node(rcv_fd, len, epfd, node, proto);
 	}
-- 
2.43.5