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 <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Tomas Glozar <[email protected]>

Author: walac

tools/tracing/rtla/src/common.c

@@ -10,7 +10,7 @@
 #include "common.h"
 
 struct trace_instance *trace_inst;
-int stop_tracing;
+volatile int stop_tracing;
 
 static void stop_trace(int sig)
 {

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;