tracing: Disable trace_printk buffer on warning too

When /proc/sys/kernel/traceoff_on_warning is set to 1, the top level
tracing buffer is disabled when a warning happens. This is very useful
when debugging and want the tracing buffer to stop taking new data when a
warning triggers keeping the events that lead up to the warning from being
overwritten.

Now that there is also a persistent ring buffer and an option to have
trace_printk go to that buffer, the same holds true for that buffer. A
warning could happen just before a crash but still write enough events to
lose the events that lead up to the first warning that was the reason for
the crash.

When /proc/sys/kernel/traceoff_on_warning is set to 1 and a warning is
triggered, not only disable the top level tracing buffer, but also disable
the buffer that trace_printk()s are written to.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Link: https://patch.msgid.link/20260121093858.5c5d7e7b@gandalf.local.home
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: rostedt

kernel/trace/trace.c

@@ -1666,9 +1666,18 @@ EXPORT_SYMBOL_GPL(tracing_off);
 void disable_trace_on_warning(void)
 {
 	if (__disable_trace_on_warning) {
+		struct trace_array *tr = READ_ONCE(printk_trace);
+
 		trace_array_printk_buf(global_trace.array_buffer.buffer, _THIS_IP_,
 			"Disabling tracing due to warning\n");
 		tracing_off();
+
+		/* Disable trace_printk() buffer too */
+		if (tr != &global_trace) {
+			trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_,
+					       "Disabling tracing due to warning\n");
+			tracer_tracing_off(tr);
+		}
 	}
 }