This happens on 64-bit big-endian machines.
SO_RCVLOWAT requires an int parameter. However, instead of int, the test
uses unsigned long in one place and size_t in another. Both are 8 bytes
long on 64-bit machines. The kernel, having received the 8 bytes, doesn't
test for the exact size of the parameter, it only cares that it's >=
sizeof(int), and casts the 4 lower-addressed bytes to an int, which, on
a big-endian machine, contains 0. 0 doesn't trigger an error, SO_RCVLOWAT
returns with success and the socket stays with the default SO_RCVLOWAT = 1,
which results in vsock_test failures, while vsock_perf doesn't even notice
that it's failed to change it.

Fixes: b1346338fbae ("vsock_test: POLLIN + SO_RCVLOWAT test")
Fixes: 542e893fbadc ("vsock/test: two tests to check credit update logic")
Fixes: 8abbffd27ced ("test/vsock: vsock_perf utility")
Signed-off-by: Konstantin Shkolnyy <kshk@linux.ibm.com>
---

Notes:
    The problem was found on s390 (big endian), while x86-64 didn't show it. After this fix, all tests pass on s390.
Changes for v3:
- fix the same problem in vsock_perf and update commit message
Changes for v2:
- add "Fixes:" lines to the commit message

 tools/testing/vsock/vsock_perf.c | 6 +++---
 tools/testing/vsock/vsock_test.c | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/tools/testing/vsock/vsock_perf.c b/tools/testing/vsock/vsock_perf.c
index 4e8578f815e0..22633c2848cc 100644
--- a/tools/testing/vsock/vsock_perf.c
+++ b/tools/testing/vsock/vsock_perf.c
@@ -133,7 +133,7 @@ static float get_gbps(unsigned long bits, time_t ns_delta)
 	       ((float)ns_delta / NSEC_PER_SEC);
 }
 
-static void run_receiver(unsigned long rcvlowat_bytes)
+static void run_receiver(int rcvlowat_bytes)
 {
 	unsigned int read_cnt;
 	time_t rx_begin_ns;
@@ -163,7 +163,7 @@ static void run_receiver(unsigned long rcvlowat_bytes)
 	printf("Listen port %u\n", port);
 	printf("RX buffer %lu bytes\n", buf_size_bytes);
 	printf("vsock buffer %lu bytes\n", vsock_buf_bytes);
-	printf("SO_RCVLOWAT %lu bytes\n", rcvlowat_bytes);
+	printf("SO_RCVLOWAT %d bytes\n", rcvlowat_bytes);
 
 	fd = socket(AF_VSOCK, SOCK_STREAM, 0);
 
@@ -439,7 +439,7 @@ static long strtolx(const char *arg)
 int main(int argc, char **argv)
 {
 	unsigned long to_send_bytes = DEFAULT_TO_SEND_BYTES;
-	unsigned long rcvlowat_bytes = DEFAULT_RCVLOWAT_BYTES;
+	int rcvlowat_bytes = DEFAULT_RCVLOWAT_BYTES;
 	int peer_cid = -1;
 	bool sender = false;
 
diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index f851f8961247..30857dd4ca97 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -833,7 +833,7 @@ static void test_stream_poll_rcvlowat_server(const struct test_opts *opts)
 
 static void test_stream_poll_rcvlowat_client(const struct test_opts *opts)
 {
-	unsigned long lowat_val = RCVLOWAT_BUF_SIZE;
+	int lowat_val = RCVLOWAT_BUF_SIZE;
 	char buf[RCVLOWAT_BUF_SIZE];
 	struct pollfd fds;
 	short poll_flags;
@@ -1282,7 +1282,7 @@ static void test_stream_rcvlowat_def_cred_upd_client(const struct test_opts *opt
 static void test_stream_credit_update_test(const struct test_opts *opts,
 					   bool low_rx_bytes_test)
 {
-	size_t recv_buf_size;
+	int recv_buf_size;
 	struct pollfd fds;
 	size_t buf_size;
 	void *buf;
-- 
2.34.1

On Fri, Oct 25, 2024 at 10:41:24AM -0500, Konstantin Shkolnyy wrote:
>This happens on 64-bit big-endian machines.
>SO_RCVLOWAT requires an int parameter. However, instead of int, the test
>uses unsigned long in one place and size_t in another. Both are 8 bytes
>long on 64-bit machines. The kernel, having received the 8 bytes, doesn't
>test for the exact size of the parameter, it only cares that it's >=
>sizeof(int), and casts the 4 lower-addressed bytes to an int, which, on
>a big-endian machine, contains 0. 0 doesn't trigger an error, SO_RCVLOWAT
>returns with success and the socket stays with the default SO_RCVLOWAT = 1,
>which results in vsock_test failures, while vsock_perf doesn't even notice
>that it's failed to change it.
>
>Fixes: b1346338fbae ("vsock_test: POLLIN + SO_RCVLOWAT test")
>Fixes: 542e893fbadc ("vsock/test: two tests to check credit update logic")
>Fixes: 8abbffd27ced ("test/vsock: vsock_perf utility")
>Signed-off-by: Konstantin Shkolnyy <kshk@linux.ibm.com>
>---
>
>Notes:
>    The problem was found on s390 (big endian), while x86-64 didn't show it. After this fix, all tests pass on s390.
>Changes for v3:
>- fix the same problem in vsock_perf and update commit message
>Changes for v2:
>- add "Fixes:" lines to the commit message

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

>
> tools/testing/vsock/vsock_perf.c | 6 +++---
> tools/testing/vsock/vsock_test.c | 4 ++--
> 2 files changed, 5 insertions(+), 5 deletions(-)
>
>diff --git a/tools/testing/vsock/vsock_perf.c b/tools/testing/vsock/vsock_perf.c
>index 4e8578f815e0..22633c2848cc 100644
>--- a/tools/testing/vsock/vsock_perf.c
>+++ b/tools/testing/vsock/vsock_perf.c
>@@ -133,7 +133,7 @@ static float get_gbps(unsigned long bits, time_t ns_delta)
> 	       ((float)ns_delta / NSEC_PER_SEC);
> }
>
>-static void run_receiver(unsigned long rcvlowat_bytes)
>+static void run_receiver(int rcvlowat_bytes)
> {
> 	unsigned int read_cnt;
> 	time_t rx_begin_ns;
>@@ -163,7 +163,7 @@ static void run_receiver(unsigned long rcvlowat_bytes)
> 	printf("Listen port %u\n", port);
> 	printf("RX buffer %lu bytes\n", buf_size_bytes);
> 	printf("vsock buffer %lu bytes\n", vsock_buf_bytes);
>-	printf("SO_RCVLOWAT %lu bytes\n", rcvlowat_bytes);
>+	printf("SO_RCVLOWAT %d bytes\n", rcvlowat_bytes);
>
> 	fd = socket(AF_VSOCK, SOCK_STREAM, 0);
>
>@@ -439,7 +439,7 @@ static long strtolx(const char *arg)
> int main(int argc, char **argv)
> {
> 	unsigned long to_send_bytes = DEFAULT_TO_SEND_BYTES;
>-	unsigned long rcvlowat_bytes = DEFAULT_RCVLOWAT_BYTES;
>+	int rcvlowat_bytes = DEFAULT_RCVLOWAT_BYTES;
> 	int peer_cid = -1;
> 	bool sender = false;
>
>diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
>index f851f8961247..30857dd4ca97 100644
>--- a/tools/testing/vsock/vsock_test.c
>+++ b/tools/testing/vsock/vsock_test.c
>@@ -833,7 +833,7 @@ static void test_stream_poll_rcvlowat_server(const struct test_opts *opts)
>
> static void test_stream_poll_rcvlowat_client(const struct test_opts *opts)
> {
>-	unsigned long lowat_val = RCVLOWAT_BUF_SIZE;
>+	int lowat_val = RCVLOWAT_BUF_SIZE;
> 	char buf[RCVLOWAT_BUF_SIZE];
> 	struct pollfd fds;
> 	short poll_flags;
>@@ -1282,7 +1282,7 @@ static void test_stream_rcvlowat_def_cred_upd_client(const struct test_opts *opt
> static void test_stream_credit_update_test(const struct test_opts *opts,
> 					   bool low_rx_bytes_test)
> {
>-	size_t recv_buf_size;
>+	int recv_buf_size;
> 	struct pollfd fds;
> 	size_t buf_size;
> 	void *buf;
>-- 
>2.34.1
>