From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Date: Fri, 8 Nov 2019 13:12:57 -0500
Subject: ftrace/x86: Add a counter to test function_graph with direct
Patch-mainline: v5.5-rc1
Git-commit: a3ad1a7e39689005cb04a4f2adb82f9d55b4724f
References: bsc#1177028

As testing for direct calls from the function graph tracer adds a little
overhead (which is a lot when tracing every function), add a counter that
can be used to test if function_graph tracer needs to test for a direct
caller or not.

It would have been nicer if we could use a static branch, but the static
branch logic fails when used within the function graph tracer trampoline.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Gary Lin <glin@suse.com>
---
 arch/x86/kernel/ftrace.c |    8 +++++---
 include/linux/ftrace.h   |    2 ++
 kernel/trace/ftrace.c    |    4 ++++
 3 files changed, 11 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -1049,9 +1049,11 @@ void prepare_ftrace_return(unsigned long
 	 * return address is actually off by one word, and we
 	 * need to adjust for that.
 	 */
-	if (ftrace_find_direct_func(self_addr + MCOUNT_INSN_SIZE)) {
-		self_addr = *parent;
-		parent++;
+	if (ftrace_direct_func_count) {
+		if (ftrace_find_direct_func(self_addr + MCOUNT_INSN_SIZE)) {
+			self_addr = *parent;
+			parent++;
+		}
 	}
 
 	/*
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -247,10 +247,12 @@ static inline void ftrace_free_mem(struc
 #endif /* CONFIG_FUNCTION_TRACER */
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+extern int ftrace_direct_func_count;
 int register_ftrace_direct(unsigned long ip, unsigned long addr);
 int unregister_ftrace_direct(unsigned long ip, unsigned long addr);
 struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr);
 #else
+# define ftrace_direct_func_count 0
 static inline int register_ftrace_direct(unsigned long ip, unsigned long addr)
 {
 	return -ENODEV;
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2363,6 +2363,7 @@ ftrace_find_tramp_ops_new(struct dyn_ftr
 /* Protected by rcu_tasks for reading, and direct_mutex for writing */
 static struct ftrace_hash *direct_functions = EMPTY_HASH;
 static DEFINE_MUTEX(direct_mutex);
+int ftrace_direct_func_count;
 
 /*
  * Search the direct_functions hash to see if the given instruction pointer
@@ -5039,6 +5040,7 @@ int register_ftrace_direct(unsigned long
 		direct->addr = addr;
 		direct->count = 0;
 		list_add_rcu(&direct->next, &ftrace_direct_funcs);
+		ftrace_direct_func_count++;
 	}
 
 	entry->ip = ip;
@@ -5064,6 +5066,7 @@ int register_ftrace_direct(unsigned long
 			if (free_hash)
 				free_ftrace_hash(free_hash);
 			free_hash = NULL;
+			ftrace_direct_func_count--;
 		}
 	} else {
 		if (!direct->count)
@@ -5124,6 +5127,7 @@ int unregister_ftrace_direct(unsigned lo
 			list_del_rcu(&direct->next);
 			synchronize_rcu_tasks();
 			kfree(direct);
+			ftrace_direct_func_count--;
 		}
 	}
  out_unlock: