selftest: memcg: skip memcg_sock test if address family not supported

[ Upstream commit 2d028f3 ]

The test_memcg_sock test in memcontrol.c sets up an IPv6 socket and send
data over it to consume memory and verify that memory.stat.sock and
memory.current values are close.

On systems where IPv6 isn't enabled or not configured to support
SOCK_STREAM, the test_memcg_sock test always fails.  When the socket()
call fails, there is no way we can test the memory consumption and verify
the above claim.  I believe it is better to just skip the test in this
case instead of reporting a test failure hinting that there may be
something wrong with the memcg code.

Link: https://lkml.kernel.org/r/20260311200526.885899-1-longman@redhat.com
Fixes: 5f8f019 ("selftests: cgroup/memcontrol: add basic test for socket accounting")
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Michal Koutný <mkoutny@suse.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Waiman-Long

tools/testing/selftests/cgroup/test_memcontrol.c

@@ -940,8 +940,11 @@ static int tcp_server(const char *cgroup, void *arg)
 	saddr.sin6_port = htons(srv_args->port);
 
 	sk = socket(AF_INET6, SOCK_STREAM, 0);
-	if (sk < 0)
+	if (sk < 0) {
+		/* Pass back errno to the ctl_fd */
+		write(ctl_fd, &errno, sizeof(errno));
 		return ret;
+	}
 
 	if (setsockopt(sk, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes)) < 0)
 		goto cleanup;
@@ -1071,6 +1074,12 @@ static int test_memcg_sock(const char *root)
 			goto cleanup;
 		close(args.ctl[0]);
 
+		/* Skip if address family not supported by protocol */
+		if (err == EAFNOSUPPORT) {
+			ret = KSFT_SKIP;
+			goto cleanup;
+		}
+
 		if (!err)
 			break;
 		if (err != EADDRINUSE)