rtla: Fix segfault in save_trace_to_file call

Running rtla with exit on threshold, but without saving trace leads to a
segmenetation fault:

$ rtla timerlat hist -T 10
...
Max timerlat IRQ latency from idle: 4.29 us in cpu 0
Segmentation fault

This is caused by null pointer deference in the call of
save_trace_to_file, which attempts to dereference an uninitialized
osnoise_tool variable:

save_trace_to_file(record->trace.inst, params->trace_output);
                   ^ this is uninitialized if params->trace_output is
                     not set

Fix this by not attempting to dereference "record" if it is NULL and
passing NULL instead. As a safety measure, the first field is also
checked for NULL inside save_trace_to_file.

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Cc: Costa Shulyupin <costa.shul@redhat.com>
Link: https://lore.kernel.org/20250313141034.299117-1-tglozar@redhat.com
Fixes: dc4d4e7 ("rtla: Refactor save_trace_to_file")
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: lenticularis39

tools/tracing/rtla/src/osnoise_hist.c

@@ -983,7 +983,8 @@ int osnoise_hist_main(int argc, char *argv[])
 
 	if (osnoise_trace_is_off(tool, record)) {
 		printf("rtla osnoise hit stop tracing\n");
-		save_trace_to_file(record->trace.inst, params->trace_output);
+		save_trace_to_file(record ? record->trace.inst : NULL,
+				   params->trace_output);
 	}
 
 out_hist:

tools/tracing/rtla/src/osnoise_top.c

@@ -813,7 +813,8 @@ int osnoise_top_main(int argc, char **argv)
 
 	if (osnoise_trace_is_off(tool, record)) {
 		printf("osnoise hit stop tracing\n");
-		save_trace_to_file(record->trace.inst, params->trace_output);
+		save_trace_to_file(record ? record->trace.inst : NULL,
+				   params->trace_output);
 	}
 
 out_top:

tools/tracing/rtla/src/timerlat_hist.c

@@ -1473,7 +1473,8 @@ int timerlat_hist_main(int argc, char *argv[])
 		if (!params->no_aa)
 			timerlat_auto_analysis(params->stop_us, params->stop_total_us);
 
-		save_trace_to_file(record->trace.inst, params->trace_output);
+		save_trace_to_file(record ? record->trace.inst : NULL,
+				   params->trace_output);
 	}
 
 out_hist:

tools/tracing/rtla/src/timerlat_top.c

@@ -1295,7 +1295,8 @@ int timerlat_top_main(int argc, char *argv[])
 		if (!params->no_aa)
 			timerlat_auto_analysis(params->stop_us, params->stop_total_us);
 
-		save_trace_to_file(record->trace.inst, params->trace_output);
+		save_trace_to_file(record ? record->trace.inst : NULL,
+				   params->trace_output);
 	} else if (params->aa_only) {
 		/*
 		 * If the trace did not stop with --aa-only, at least print the

tools/tracing/rtla/src/trace.c

@@ -75,7 +75,7 @@ int save_trace_to_file(struct tracefs_instance *inst, const char *filename)
 	int out_fd, in_fd;
 	int retval = -1;
 
-	if (!filename)
+	if (!inst || !filename)
 		return 0;
 
 	in_fd = tracefs_instance_file_open(inst, file, O_RDONLY);