tracing: Annotate ftrace_graph_notrace_hash pointer with __rcu

Fix following instances of sparse error
kernel/trace/ftrace.c:5667:29: error: incompatible types in comparison
kernel/trace/ftrace.c:5813:21: error: incompatible types in comparison
kernel/trace/ftrace.c:5868:36: error: incompatible types in comparison
kernel/trace/ftrace.c:5870:25: error: incompatible types in comparison

Use rcu_dereference_protected to dereference the newly annotated pointer.

Link: http://lkml.kernel.org/r/20200205055701.30195-1-frextrite@gmail.comSigned-off-by: Amol Grover <frextrite@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -5592,7 +5592,7 @@ static const struct file_operations ftrace_notrace_fops = {
 static DEFINE_MUTEX(graph_lock);
 
 struct ftrace_hash __rcu *ftrace_graph_hash = EMPTY_HASH;
-struct ftrace_hash *ftrace_graph_notrace_hash = EMPTY_HASH;
+struct ftrace_hash __rcu *ftrace_graph_notrace_hash = EMPTY_HASH;
 
 enum graph_filter_type {
 	GRAPH_FILTER_NOTRACE	= 0,

kernel/trace/trace.h

@@ -965,7 +965,7 @@ extern void __trace_graph_return(struct trace_array *tr,
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 extern struct ftrace_hash __rcu *ftrace_graph_hash;
-extern struct ftrace_hash *ftrace_graph_notrace_hash;
+extern struct ftrace_hash __rcu *ftrace_graph_notrace_hash;
 
 static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace)
 {
@@ -1018,10 +1018,14 @@ static inline void ftrace_graph_addr_finish(struct ftrace_graph_ret *trace)
 static inline int ftrace_graph_notrace_addr(unsigned long addr)
 {
 	int ret = 0;
+	struct ftrace_hash *notrace_hash;
 
 	preempt_disable_notrace();
 
-	if (ftrace_lookup_ip(ftrace_graph_notrace_hash, addr))
+	notrace_hash = rcu_dereference_protected(ftrace_graph_notrace_hash,
+						 !preemptible());
+
+	if (ftrace_lookup_ip(notrace_hash, addr))
 		ret = 1;
 
 	preempt_enable_notrace();