linux-kernel - [PATCH v2 15/18] rtla: Make stop

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Message-ID: <20260106133655.249887-16-wander@redhat.com>
Date: Tue,  6 Jan 2026 08:49:51 -0300
From: Wander Lairson Costa <wander@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>,
	Tomas Glozar <tglozar@...hat.com>,
	Wander Lairson Costa <wander@...hat.com>,
	Crystal Wood <crwood@...hat.com>,
	Ivan Pravdin <ipravdin.official@...il.com>,
	Costa Shulyupin <costa.shul@...hat.com>,
	John Kacur <jkacur@...hat.com>,
	Tiezhu Yang <yangtiezhu@...ngson.cn>,
	linux-trace-kernel@...r.kernel.org (open list:Real-time Linux Analysis (RTLA) tools),
	linux-kernel@...r.kernel.org (open list:Real-time Linux Analysis (RTLA) tools),
	bpf@...r.kernel.org (open list:BPF [MISC]:Keyword:(?:\b|_)bpf(?:\b|_))
Subject: [PATCH v2 15/18] rtla: Make stop_tracing variable volatile

The stop_tracing global variable is accessed from both the signal
handler context and the main program flow without synchronization.
This creates a potential race condition where compiler optimizations
could cache the variable value in registers, preventing the signal
handler's updates from being visible to other parts of the program.

Add the volatile qualifier to stop_tracing in both common.c and
common.h to ensure all accesses to this variable bypass compiler
optimizations and read directly from memory. This guarantees that
when the signal handler sets stop_tracing, the change is immediately
visible to the main program loop, preventing potential hangs or
delayed shutdown when termination signals are received.

Signed-off-by: Wander Lairson Costa <wander@...hat.com>
---
 tools/tracing/rtla/src/common.c | 2 +-
 tools/tracing/rtla/src/common.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/tracing/rtla/src/common.c b/tools/tracing/rtla/src/common.c
index d608ffe12e7b0..1e6542a1e9630 100644
--- a/tools/tracing/rtla/src/common.c
+++ b/tools/tracing/rtla/src/common.c
@@ -8,7 +8,7 @@
 #include "common.h"
 
 struct trace_instance *trace_inst;
-int stop_tracing;
+volatile int stop_tracing;
 
 static void stop_trace(int sig)
 {
diff --git a/tools/tracing/rtla/src/common.h b/tools/tracing/rtla/src/common.h
index f2c9e21c03651..283641f3e7c9b 100644
--- a/tools/tracing/rtla/src/common.h
+++ b/tools/tracing/rtla/src/common.h
@@ -54,7 +54,7 @@ struct osnoise_context {
 };
 
 extern struct trace_instance *trace_inst;
-extern int stop_tracing;
+extern volatile int stop_tracing;
 
 struct hist_params {
 	char			no_irq;
-- 
2.52.0