syscalls/msgstress01: Fix the stop logic

The stop flag didn't really work because:

- if queue is full msgsnd() will block in the kernel
- if queue is empty msgrcv() will block in the kernel

And if the other process from the reader-writer pair exits the queue
will be never changed and the test will get stuck and killed by watchdog
timer.

What we need to do is to use IPC_NOWAIT, retry manually (after short
usleep) and handle errors manually as well. In that case no processes
will sleep in kernel and setting the stop flag will actually stop the
test.

Link: https://lore.kernel.org/ltp/[email protected]/
Acked-by: Andrea Cervesato <[email protected]>
Reviewed-by: Martin Doucha <[email protected]>
Reviewed-by: Petr Vorel <[email protected]>
Signed-off-by: Cyril Hrubis <[email protected]>

Author: metan-ucw

testcases/kernel/syscalls/ipc/msgstress/msgstress01.c

@@ -101,8 +101,18 @@ static void writer(const int id, const int pos)
 	struct sysv_data *buff = &ipc_data[pos];
 	int iter = num_iterations;
 
-	while (--iter >= 0 && !(*stop))
-		SAFE_MSGSND(id, &buff->msg, 100, 0);
+	while (--iter >= 0 && !(*stop)) {
+		int size = msgsnd(id, &buff->msg, 100, IPC_NOWAIT);
+
+		if (size < 0) {
+			if (errno == EAGAIN) {
+				usleep(10);
+				continue;
+			}
+
+			tst_brk(TBROK | TERRNO, "msgsnd() failed");
+		}
+	}
 }
 
 static void reader(const int id, const int pos)
@@ -115,7 +125,15 @@ static void reader(const int id, const int pos)
 	while (--iter >= 0 && !(*stop)) {
 		memset(&msg_recv, 0, sizeof(struct sysv_msg));
 
-		size = SAFE_MSGRCV(id, &msg_recv, 100, MSGTYPE, 0);
+		size = msgrcv(id, &msg_recv, 100, MSGTYPE, IPC_NOWAIT);
+		if (size < 0) {
+			if (errno == ENOMSG) {
+				usleep(10);
+				continue;
+			}
+
+			tst_brk(TBROK | TERRNO, "msgrcv() failed");
+		}
 
 		if (msg_recv.type != buff->msg.type) {
 			tst_res(TFAIL, "Received the wrong message type");
@@ -152,6 +170,7 @@ static void remove_queues(void)
 {
 	for (int pos = 0; pos < num_messages; pos++) {
 		struct sysv_data *buff = &ipc_data[pos];
+
 		if (buff->id != -1)
 			SAFE_MSGCTL(buff->id, IPC_RMID, NULL);
 	}