[PATCH v1] rt-tests: Exit with failure when breaktrace threshold is exceeded

cyclictest and cyclicdeadline always exit 0 even when the latency
threshold set by --breaktrace is exceeded, requiring test harnesses
to parse output or json to detect a failed test.

Set ret to EXIT_FAILURE when break_thread_id is set, indicating the
breaktrace threshold was hit.  The exit code enables shell expressions
like "cyclictest ... && echo PASS" and seamless integration with testing
frameworks.  Also pass ret to rt_write_json() in cyclicdeadline so the
JSON output reflects the failure.

Assisted-by: Claude:claude-opus-4-6
---
 src/cyclictest/cyclictest.8         | 8 ++++++++
 src/cyclictest/cyclictest.c         | 1 +
 src/sched_deadline/cyclicdeadline.8 | 8 ++++++++
 src/sched_deadline/cyclicdeadline.c | 7 +++++--
 4 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/cyclictest/cyclictest.8 b/src/cyclictest/cyclictest.8
index fc6121aa4d47..813c61653f61 100644
--- a/src/cyclictest/cyclictest.8
+++ b/src/cyclictest/cyclictest.8
@@ -311,6 +311,14 @@ in mind, below cyclictest example invocation can provide a good start:
    --histfile=output.txt
 .fi
 .
+.SH "Exit status"
+.TP
+.B 0
+Success - all latencies were within the breaktrace threshold, or no threshold was set.
+.TP
+.B 1
+Failure - a latency exceeding the breaktrace threshold was detected.
+.
 .SH "See also"
 .MR numa 3 ,
 .MR numactl 8 ,
diff --git a/src/cyclictest/cyclictest.c b/src/cyclictest/cyclictest.c
index 71cf5cb25c22..88fc08347cba 100644
--- a/src/cyclictest/cyclictest.c
+++ b/src/cyclictest/cyclictest.c
@@ -2337,6 +2337,7 @@ int main(int argc, char **argv)
 		if (break_thread_id) {
 			printf("# Break thread: %d\n", break_thread_id);
 			printf("# Break value: %llu\n", (unsigned long long)break_thread_value);
+			ret = EXIT_FAILURE;
 		}
 	}
 
diff --git a/src/sched_deadline/cyclicdeadline.8 b/src/sched_deadline/cyclicdeadline.8
index bfc6327c51da..cd7088629d97 100644
--- a/src/sched_deadline/cyclicdeadline.8
+++ b/src/sched_deadline/cyclicdeadline.8
@@ -58,6 +58,14 @@ Send break trace command when latency > USEC
 .B \-\-tracemark
 write a trace mark when \-b latency is exceeded.
 .br
+.SH "Exit status"
+.TP
+.B 0
+Success - all latencies were within the breaktrace threshold, or no threshold was set.
+.TP
+.B 1
+Failure - a latency exceeding the breaktrace threshold was detected.
+.
 .SH AUTHOR
 cyclicdeadline was written by Steven Rostedt <[email protected]>
 .PP
diff --git a/src/sched_deadline/cyclicdeadline.c b/src/sched_deadline/cyclicdeadline.c
index 0c6c96976010..1123de4f4cae 100644
--- a/src/sched_deadline/cyclicdeadline.c
+++ b/src/sched_deadline/cyclicdeadline.c
@@ -1315,10 +1315,13 @@ int main(int argc, char **argv)
 
 	loop(sched_data, nr_threads);
 
+	ret = EXIT_SUCCESS;
+
 	if (tracelimit) {
 		if (break_thread_id) {
 			printf("# Break thread: %d\n", break_thread_id);
 			printf("# Break value: %llu\n", (unsigned long long)break_thread_value);
+			ret = EXIT_FAILURE;
 		}
 	}
 
@@ -1334,7 +1337,7 @@ int main(int argc, char **argv)
 	}
 
 	if (strlen(jsonfile) != 0)
-		rt_write_json(jsonfile, 0, write_stats, sched_data);
+		rt_write_json(jsonfile, ret, write_stats, sched_data);
 
 	if (setcpu_buf)
 		free(setcpu_buf);
@@ -1344,5 +1347,5 @@ int main(int argc, char **argv)
 		fclose(histfile);
 	hset_destroy(&hset);
 
-	return 0;
+	return ret;
 }
-- 
2.54.0