Add test kernel ring overflow test for nOS-V

There is a problem in the way we are reading the buffer in nOS-V, which
fails when the ring buffer gets full. This regression test ensures it is
fixed.

Reported-by: David Álvarez <david.alvarez@bsc.es>

test/rt/nosv/CMakeLists.txt

@@ -44,6 +44,7 @@ nosv_test(parallel-tasks.c SORT)
 nosv_test(inline.c SORT)
 nosv_test(mutex.c SORT LEVEL 3)
 nosv_test(barrier.c SORT LEVEL 3)
+nosv_test(overflow-kernel-ring.c SORT LEVEL 3)
 
 # Test multiple instrumentation levels
 nosv_test(several-tasks.c SORT NAME several-tasks-level-0 LEVEL 0)

test/rt/nosv/overflow-kernel-ring.c

@@ -0,0 +1,77 @@
+/* Copyright (c) 2024 Barcelona Supercomputing Center (BSC)
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <nosv.h>
+#include <nosv/affinity.h>
+#include <stdatomic.h>
+#include <unistd.h>
+
+#include "common.h"
+#include "compat.h"
+
+int done = 0;
+
+/* https://gitlab.bsc.es/nos-v/nos-v/-/blob/master/src/include/instr.h?ref_type=heads#L542 */
+#define NOSV_INSTR_KBUFLEN (4UL * 1024UL * 1024UL) // 4 MB
+
+static void
+task_run(nosv_task_t task)
+{
+	UNUSED(task);
+
+	/* Cause enough context switches for the kernel ring to be full,
+	 * which wouldn't fail if nosv_waitfor() flushes the kernel
+	 * events. */
+
+	unsigned long fill = 3 * NOSV_INSTR_KBUFLEN / 4;
+	unsigned long n = fill / 16;
+
+	struct timespec one_ns = { .tv_sec = 0, .tv_nsec = 1 };
+
+	for (unsigned long run = 0; run < 3; run++) {
+		info("starting run %lu", run);
+		for (unsigned long i = 0; i < n; i++)
+			nanosleep(&one_ns, NULL);
+
+		info("starting waitfor");
+
+		if (nosv_waitfor(1, NULL) != 0)
+			die("nosv_waitfor failed");
+
+		info("end run %lu", run);
+	}
+
+	done = 1;
+}
+
+int main(void)
+{
+	if (nosv_init())
+		die("nosv_init failed");
+
+	nosv_task_type_t task_type;
+	if (nosv_type_init(&task_type, task_run, NULL, NULL, "task", NULL, NULL, NOSV_TYPE_INIT_NONE))
+		die("nosv_type_init failed");
+
+	nosv_task_t task;
+	if (nosv_create(&task, task_type, 0, NOSV_CREATE_NONE))
+		die("nosv_create failed");
+
+	if (nosv_submit(task, NOSV_SUBMIT_IMMEDIATE))
+		die("nosv_submit failed");
+
+	/* Wait for the task to finish */
+	while (!done)
+		sleep_us(10000);
+
+	if (nosv_destroy(task, NOSV_DESTROY_NONE))
+		die("nosv_destroy failed");
+
+	if (nosv_type_destroy(task_type, NOSV_TYPE_DESTROY_NONE))
+		die("nosv_type_destroy failed");
+
+	if (nosv_shutdown())
+		die("nosv_shutdown failed");
+
+	return 0;
+}