[PATCH net] vsock/test: Fix occasional failure in SOCK_STREAM SHUT_RD test

[Konstantin Shkolnyy <kshk@linux.ibm.com>]

The test outputs:
"SOCK_STREAM SHUT_RD...expected send(2) failure, got 1".

It tests that shutdown(fd, SHUT_RD) on one side causes send() to fail on
the other side. However, sometimes there is a delay in delivery of the
SHUT_RD command, send() succeeds and the test fails, even though the
command is properly delivered and send() starts failing several
milliseconds later.

The delay occurs in the kernel because the used buffer notification
callback virtio_vsock_rx_done(), called upon receipt of the SHUT_RD
command, doesn't immediately disable send(). It delegates that to
a kernel thread (via vsock->rx_work). Sometimes that thread is delayed
more than the test expects.

Change the test to keep calling send() until it fails or a timeout occurs.

Fixes: b698bd97c5711 ("test/vsock: shutdowned socket test")
Signed-off-by: Konstantin Shkolnyy <kshk@linux.ibm.com>
---
 tools/testing/vsock/vsock_test.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index 613551132a96..c3b90a94a281 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -1058,17 +1058,22 @@ static void sigpipe(int signo)
 	have_sigpipe = 1;
 }
 
-static void test_stream_check_sigpipe(int fd)
+static void test_for_send_failure(int fd, int send_flags)
 {
-	ssize_t res;
+	timeout_begin(TIMEOUT);
+	while (true) {
+		if (send(fd, "A", 1, send_flags) == -1)
+			return;
+		timeout_check("expected send(2) failure");
+	}
+	timeout_end();
+}
 
+static void test_stream_check_sigpipe(int fd)
+{
 	have_sigpipe = 0;
 
-	res = send(fd, "A", 1, 0);
-	if (res != -1) {
-		fprintf(stderr, "expected send(2) failure, got %zi\n", res);
-		exit(EXIT_FAILURE);
-	}
+	test_for_send_failure(fd, 0);
 
 	if (!have_sigpipe) {
 		fprintf(stderr, "SIGPIPE expected\n");
@@ -1077,11 +1082,7 @@ static void test_stream_check_sigpipe(int fd)
 
 	have_sigpipe = 0;
 
-	res = send(fd, "A", 1, MSG_NOSIGNAL);
-	if (res != -1) {
-		fprintf(stderr, "expected send(2) failure, got %zi\n", res);
-		exit(EXIT_FAILURE);
-	}
+	test_for_send_failure(fd, MSG_NOSIGNAL);
 
 	if (have_sigpipe) {
 		fprintf(stderr, "SIGPIPE not expected\n");
-- 
2.34.1