tracing: Dump stacktrace trigger to the corresponding instance

The stacktrace event trigger is not dumping the stacktrace to the instance
where it was enabled, but to the global "instance."

Use the private_data, pointing to the trigger file, to figure out the
corresponding trace instance, and use it in the trigger action, like
snapshot_trigger does.

Link: https://lkml.kernel.org/r/afbb0b4f18ba92c276865bc97204d438473f4ebc.1645396236.git.bristot@kernel.org

Cc: stable@vger.kernel.org
Fixes: ae63b31e ("tracing: Separate out trace events from global variables")
Reviewed-by: NTom Zanussi <zanussi@kernel.org>
Tested-by: NTom Zanussi <zanussi@kernel.org>
Signed-off-by: NDaniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: NSteven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/trace_events_trigger.c

@@ -1540,6 +1540,11 @@ stacktrace_trigger(struct event_trigger_data *data,
 		   struct trace_buffer *buffer,  void *rec,
 		   struct ring_buffer_event *event)
 {
+	struct trace_event_file *file = data->private_data;
+
+	if (file)
+		__trace_stack(file->tr, tracing_gen_ctx(), STACK_SKIP);
+	else
 		trace_dump_stack(STACK_SKIP);
 }