From: Stefano Garzarella <sgarzare@redhat.com>

When the other peer calls shutdown(SHUT_RD), there is a chance that
the send() call could occur before the message carrying the close
information arrives over the transport. In such cases, the send()
might still succeed. To avoid this race, let's retry the send() call
a few times, ensuring the test is more reliable.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 tools/testing/vsock/vsock_test.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index d0f6d253ac72..7de870dee1cf 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -1064,11 +1064,18 @@ 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);
-	}
+	/* When the other peer calls shutdown(SHUT_RD), there is a chance that
+	 * the send() call could occur before the message carrying the close
+	 * information arrives over the transport. In such cases, the send()
+	 * might still succeed. To avoid this race, let's retry the send() call
+	 * a few times, ensuring the test is more reliable.
+	 */
+	timeout_begin(TIMEOUT);
+	do {
+		res = send(fd, "A", 1, 0);
+		timeout_check("send");
+	} while (res != -1);
+	timeout_end();
 
 	if (!have_sigpipe) {
 		fprintf(stderr, "SIGPIPE expected\n");
@@ -1077,11 +1084,12 @@ 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);
-	}
+	timeout_begin(TIMEOUT);
+	do {
+		res = send(fd, "A", 1, MSG_NOSIGNAL);
+		timeout_check("send");
+	} while (res != -1);
+	timeout_end();
 
 	if (have_sigpipe) {
 		fprintf(stderr, "SIGPIPE not expected\n");
-- 
2.49.0

On 5/8/25 4:20 PM, Stefano Garzarella wrote:
> From: Stefano Garzarella <sgarzare@redhat.com>
> 
> When the other peer calls shutdown(SHUT_RD), there is a chance that
> the send() call could occur before the message carrying the close
> information arrives over the transport. In such cases, the send()
> might still succeed. To avoid this race, let's retry the send() call
> a few times, ensuring the test is more reliable.
> 
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  tools/testing/vsock/vsock_test.c | 28 ++++++++++++++++++----------
>  1 file changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
> index d0f6d253ac72..7de870dee1cf 100644
> --- a/tools/testing/vsock/vsock_test.c
> +++ b/tools/testing/vsock/vsock_test.c
> @@ -1064,11 +1064,18 @@ 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);
> -	}
> +	/* When the other peer calls shutdown(SHUT_RD), there is a chance that
> +	 * the send() call could occur before the message carrying the close
> +	 * information arrives over the transport. In such cases, the send()
> +	 * might still succeed. To avoid this race, let's retry the send() call
> +	 * a few times, ensuring the test is more reliable.
> +	 */
> +	timeout_begin(TIMEOUT);
> +	do {
> +		res = send(fd, "A", 1, 0);
> +		timeout_check("send");
> +	} while (res != -1);

AFAICS the above could spin on send() for up to 10s, I would say
considerably more than 'a few times' ;)

In practice that could cause side effect on the timing of other
concurrent tests (due to one CPU being 100% used for a while).

What if the peer rcvbuf fills-up: will the send fail? That could cause
false-negative.

I *think* it should be better to insert a short sleep in the loop.

/P

On Tue, May 13, 2025 at 12:37:36PM +0200, Paolo Abeni wrote:
>On 5/8/25 4:20 PM, Stefano Garzarella wrote:
>> From: Stefano Garzarella <sgarzare@redhat.com>
>>
>> When the other peer calls shutdown(SHUT_RD), there is a chance that
>> the send() call could occur before the message carrying the close
>> information arrives over the transport. In such cases, the send()
>> might still succeed. To avoid this race, let's retry the send() call
>> a few times, ensuring the test is more reliable.
>>
>> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>> ---
>>  tools/testing/vsock/vsock_test.c | 28 ++++++++++++++++++----------
>>  1 file changed, 18 insertions(+), 10 deletions(-)
>>
>> diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
>> index d0f6d253ac72..7de870dee1cf 100644
>> --- a/tools/testing/vsock/vsock_test.c
>> +++ b/tools/testing/vsock/vsock_test.c
>> @@ -1064,11 +1064,18 @@ 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);
>> -	}
>> +	/* When the other peer calls shutdown(SHUT_RD), there is a chance that
>> +	 * the send() call could occur before the message carrying the close
>> +	 * information arrives over the transport. In such cases, the send()
>> +	 * might still succeed. To avoid this race, let's retry the send() call
>> +	 * a few times, ensuring the test is more reliable.
>> +	 */
>> +	timeout_begin(TIMEOUT);
>> +	do {
>> +		res = send(fd, "A", 1, 0);
>> +		timeout_check("send");
>> +	} while (res != -1);
>
>AFAICS the above could spin on send() for up to 10s, I would say
>considerably more than 'a few times' ;)
>
>In practice that could cause side effect on the timing of other
>concurrent tests (due to one CPU being 100% used for a while).
>
>What if the peer rcvbuf fills-up: will the send fail? That could cause
>false-negative.

Good point!

>
>I *think* it should be better to insert a short sleep in the loop.

Agree, I'll add.

Thanks,
Stefano