tracing: Add tracer_tracing_disable/enable() functions

Allow a tracer to disable writing to its buffer for a temporary amount of
time and re-enable it.

The tracer_tracing_disable() will disable writing to the trace array
buffer, and requires a tracer_tracing_enable() to re-enable it.

The difference between tracer_tracing_disable() and tracer_tracing_off()
is that the disable version can nest, and requires as many enable() calls
as disable() calls to re-enable the buffer. Where as the off() function
can be called multiple times and only requires a singe tracer_tracing_on()
to re-enable the buffer.

Cc: Jason Wessel <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Daniel Thompson <[email protected]>
Reviewed-by: Douglas Anderson <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: rostedt

kernel/trace/trace.c

@@ -1582,6 +1582,39 @@ void tracer_tracing_off(struct trace_array *tr)
 	smp_wmb();
 }
 
+/**
+ * tracer_tracing_disable() - temporary disable the buffer from write
+ * @tr: The trace array to disable its buffer for
+ *
+ * Expects trace_tracing_enable() to re-enable tracing.
+ * The difference between this and tracer_tracing_off() is that this
+ * is a counter and can nest, whereas, tracer_tracing_off() can
+ * be called multiple times and a single trace_tracing_on() will
+ * enable it.
+ */
+void tracer_tracing_disable(struct trace_array *tr)
+{
+	if (WARN_ON_ONCE(!tr->array_buffer.buffer))
+		return;
+
+	ring_buffer_record_disable(tr->array_buffer.buffer);
+}
+
+/**
+ * tracer_tracing_enable() - counter part of tracer_tracing_disable()
+ * @tr: The trace array that had tracer_tracincg_disable() called on it
+ *
+ * This is called after tracer_tracing_disable() has been called on @tr,
+ * when it's safe to re-enable tracing.
+ */
+void tracer_tracing_enable(struct trace_array *tr)
+{
+	if (WARN_ON_ONCE(!tr->array_buffer.buffer))
+		return;
+
+	ring_buffer_record_enable(tr->array_buffer.buffer);
+}
+
 /**
  * tracing_off - turn off tracing buffers
  *

kernel/trace/trace.h

@@ -665,6 +665,8 @@ bool tracing_is_disabled(void);
 bool tracer_tracing_is_on(struct trace_array *tr);
 void tracer_tracing_on(struct trace_array *tr);
 void tracer_tracing_off(struct trace_array *tr);
+void tracer_tracing_disable(struct trace_array *tr);
+void tracer_tracing_enable(struct trace_array *tr);
 struct dentry *trace_create_file(const char *name,
 				 umode_t mode,
 				 struct dentry *parent,