Fix for nOS-V with ovni.level=2

When running without all the subsystem events enabled in nOS-V, it is
possible to emit two consecutive VTx events, which would push twice the
same value ST_TASK_BODY into the subsystem channel. This change relaxes
the subsystem channel to accept duplicate stacked values. A regression
test is also added.

Reported-By: Raúl Peñacoba Veigas <raul.penacoba@bsc.es>

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- Fix emulation for level 2 or lower in nOS-V with inline tasks by
+  allowing duplicates in the subsystem channel.
+
 ## [1.4.0] - 2023-11-08
 
 ### Added

src/emu/nosv/setup.c

@@ -57,6 +57,9 @@ static const int chan_dup[CH_MAX] = {
 	[CH_APPID] = 1,
 	[CH_TYPE] = 1,
 	[CH_RANK] = 1,
+	/* Can push twice ST_TASK_BODY if we run without subsystem
+	 * events (level 2). */
+	[CH_SUBSYSTEM] = 1,
 };
 
 /* ----------------- pvt ------------------ */

test/emu/nosv/CMakeLists.txt

@@ -10,3 +10,4 @@ test_emu(mp-rank.c MP)
 test_emu(switch-same-type.c)
 test_emu(multiple-segment.c MP NPROC 4)
 test_emu(task-pause-from-submit.c)
+test_emu(same-subsystem.c)

test/emu/nosv/same-subsystem.c

@@ -0,0 +1,30 @@
+/* Copyright (c) 2023 Barcelona Supercomputing Center (BSC)
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <stdint.h>
+#include "compat.h"
+#include "instr.h"
+#include "instr_nosv.h"
+
+/* With the introduction of ovni.level in nOS-V, we can have the
+ * situation in which two VTx events are emitted without the subsystem
+ * events. This causes the subsystem channel to push twice the same
+ * value ST_TASK_BODY. */
+
+int
+main(void)
+{
+	instr_start(0, 1);
+
+	instr_nosv_type_create(10);
+	instr_nosv_task_create(1, 10);
+	instr_nosv_task_create(2, 10);
+	instr_nosv_task_execute(1);
+	instr_nosv_task_execute(2);
+	instr_nosv_task_end(2);
+	instr_nosv_task_end(1);
+
+	instr_end();
+
+	return 0;
+}