tracing: Stop current tracer when resizing buffer

When the ring buffer is being resized, it can cause side effects to the
running tracer. For instance, there's a race with irqsoff tracer that
swaps individual per cpu buffers between the main buffer and the snapshot
buffer. The resize operation modifies the main buffer and then the
snapshot buffer. If a swap happens in between those two operations it will
break the tracer.

Simply stop the running tracer before resizing the buffers and enable it
again when finished.

Link: https://lkml.kernel.org/r/[email protected]

Cc: [email protected]
Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Fixes: 3928a8a ("ftrace: make work with new ring buffer")
Signed-off-by: Steven Rostedt (Google) <[email protected]>

kernel/trace/trace.c

@@ -6387,9 +6387,12 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr,
 	if (!tr->array_buffer.buffer)
 		return 0;
 
+	/* Do not allow tracing while resizng ring buffer */
+	tracing_stop_tr(tr);
+
 	ret = ring_buffer_resize(tr->array_buffer.buffer, size, cpu);
 	if (ret < 0)
-		return ret;
+		goto out_start;
 
 #ifdef CONFIG_TRACER_MAX_TRACE
 	if (!tr->current_trace->use_max_tr)
@@ -6417,7 +6420,7 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr,
 			WARN_ON(1);
 			tracing_disabled = 1;
 		}
-		return ret;
+		goto out_start;
 	}
 
 	update_buffer_entries(&tr->max_buffer, cpu);
@@ -6426,7 +6429,8 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr,
 #endif /* CONFIG_TRACER_MAX_TRACE */
 
 	update_buffer_entries(&tr->array_buffer, cpu);
-
+ out_start:
+	tracing_start_tr(tr);
 	return ret;
 }