tracing: Make printk_trace global for tracing system

The printk_trace is used to determine which trace_array trace_printk()
writes to. By making it a global variable among the tracing subsystem it
will allow the trace_printk functions to be moved out of trace.c and still
have direct access to that variable.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://patch.msgid.link/20260208032450.144525891@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: rostedt

kernel/trace/trace.c

@@ -534,7 +534,7 @@ static struct trace_array global_trace = {
 	.trace_flags = TRACE_DEFAULT_FLAGS,
 };
 
-static struct trace_array *printk_trace = &global_trace;
+struct trace_array *printk_trace = &global_trace;
 
 /* List of trace_arrays interested in the top level trace_marker */
 static LIST_HEAD(marker_copies);

kernel/trace/trace.h

@@ -482,6 +482,8 @@ extern bool trace_clock_in_ns(struct trace_array *tr);
 
 extern unsigned long trace_adjust_address(struct trace_array *tr, unsigned long addr);
 
+extern struct trace_array *printk_trace;
+
 /*
  * The global tracer (top) should be the first trace array added,
  * but we check the flag anyway.