linux-kernel - [PATCH 2/5] rtla/timerlat_hist: Stop timerlat tracer on signal

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Message-ID: <20250116144931.649593-3-tglozar@redhat.com>
Date: Thu, 16 Jan 2025 15:49:28 +0100
From: Tomas Glozar <tglozar@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-trace-kernel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	John Kacur <jkacur@...hat.com>,
	Luis Goncalves <lgoncalv@...hat.com>,
	Gabriele Monaco <gmonaco@...hat.com>,
	Tomas Glozar <tglozar@...hat.com>
Subject: [PATCH 2/5] rtla/timerlat_hist: Stop timerlat tracer on signal

Currently, when either SIGINT from the user or SIGALRM from the duration
timer is caught by rtla-timerlat, stop_tracing is set to break out of
the main loop. This is not sufficient for cases where the timerlat
tracer is producing more data than rtla can consume, since in that case,
rtla is looping indefinitely inside tracefs_iterate_raw_events, never
reaches the check of stop_tracing and hangs.

In addition to setting stop_tracing, also stop the timerlat tracer on
received signal (SIGINT or SIGALRM). This will stop new samples so that
the existing samples may be processed and tracefs_iterate_raw_events
eventually exits.

Cc: stable@...r.kernel.org
Fixes: 1eeb6328e8b3 ("rtla/timerlat: Add timerlat hist mode")
Signed-off-by: Tomas Glozar <tglozar@...hat.com>
---
 tools/tracing/rtla/src/timerlat_hist.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/tracing/rtla/src/timerlat_hist.c b/tools/tracing/rtla/src/timerlat_hist.c
index 4403cc4eba30..e8d249e22251 100644
--- a/tools/tracing/rtla/src/timerlat_hist.c
+++ b/tools/tracing/rtla/src/timerlat_hist.c
@@ -1146,9 +1146,12 @@ static struct osnoise_tool
 }
 
 static int stop_tracing;
+static struct trace_instance *hist_inst = NULL;
 static void stop_hist(int sig)
 {
 	stop_tracing = 1;
+	if (hist_inst)
+		trace_instance_stop(hist_inst);
 }
 
 /*
@@ -1195,6 +1198,12 @@ int timerlat_hist_main(int argc, char *argv[])
 	}
 
 	trace = &tool->trace;
+	/*
+	 * Save trace instance into global variable so that SIGINT can stop
+	 * the timerlat tracer.
+	 * Otherwise, rtla could loop indefinitely when overloaded.
+	 */
+	hist_inst = trace;
 
 	retval = enable_timerlat(trace);
 	if (retval) {
@@ -1363,7 +1372,7 @@ int timerlat_hist_main(int argc, char *argv[])
 
 	return_value = 0;
 
-	if (trace_is_off(&tool->trace, &record->trace)) {
+	if (trace_is_off(&tool->trace, &record->trace) && !stop_tracing) {
 		printf("rtla timerlat hit stop tracing\n");
 
 		if (!params->no_aa)
-- 
2.47.1