selftests: tls: avoid flakiness in data_steal

We see the following failure a few times a week:

  #  RUN           global.data_steal ...
  # tls.c:3280:data_steal:Expected recv(cfd, buf2, sizeof(buf2), MSG_DONTWAIT) (10000) == -1 (-1)
  # data_steal: Test failed
  #          FAIL  global.data_steal
  not ok 8 global.data_steal

The 10000 bytes read suggests that the child process did a recv()
of half of the data using the TLS ULP and we're now getting the
remaining half. The intent of the test is to get the child to
enter _TCP_ recvmsg handler, so it needs to enter the syscall before
parent installed the TLS recvmsg with setsockopt(SOL_TLS).

Instead of the 10msec sleep send 1 byte of data and wait for the
child to consume it.

Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20260106200205.1593915-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/testing/selftests/net/tls.c b/tools/testing/selftests/net/tls.c
index a4d16a460fbe49733b302f086c3ba6bd0ba53622..9e2ccea13d7023a977aa853ff6e3531166e48fb8 100644 (file)
--- a/tools/testing/selftests/net/tls.c
+++ b/tools/testing/selftests/net/tls.c
@@ -3260,17 +3260,25 @@ TEST(data_steal) {
        ASSERT_EQ(setsockopt(cfd, IPPROTO_TCP, TCP_ULP, "tls", sizeof("tls")), 0);
 
        /* Spawn a child and get it into the read wait path of the underlying
-        * TCP socket.
+        * TCP socket (before kernel .recvmsg is replaced with the TLS one).
         */
        pid = fork();
        ASSERT_GE(pid, 0);
        if (!pid) {
-               EXPECT_EQ(recv(cfd, buf, sizeof(buf) / 2, MSG_WAITALL),
-                         sizeof(buf) / 2);
+               EXPECT_EQ(recv(cfd, buf, sizeof(buf) / 2 + 1, MSG_WAITALL),
+                         sizeof(buf) / 2 + 1);
                exit(!__test_passed(_metadata));
        }
 
-       usleep(10000);
+       /* Send a sync byte and poll until it's consumed to ensure
+        * the child is in recv() before we proceed to install TLS.
+        */
+       ASSERT_EQ(send(fd, buf, 1, 0), 1);
+       do {
+               usleep(500);
+       } while (recv(cfd, buf, 1, MSG_PEEK | MSG_DONTWAIT) == 1);
+       EXPECT_EQ(errno, EAGAIN);
+
        ASSERT_EQ(setsockopt(fd, SOL_TLS, TLS_TX, &tls, tls.len), 0);
        ASSERT_EQ(setsockopt(cfd, SOL_TLS, TLS_RX, &tls, tls.len), 0);