Commit a3ad1a7e authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

ftrace/x86: Add a counter to test function_graph with direct 



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: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 562955fe

arch/x86/kernel/ftrace.c

+5 −3
Original line number Diff line number Diff line
@@ -1049,10 +1049,12 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, 
	 * return address is actually off by one word, and we

	 * need to adjust for that.

	 */

	if (ftrace_direct_func_count) {

		if (ftrace_find_direct_func(self_addr + MCOUNT_INSN_SIZE)) {

			self_addr = *parent;

			parent++;

		}

	}



	/*

	 * Protect against fault, even if it shouldn't

include/linux/ftrace.h

+2 −0
Original line number Diff line number Diff line
@@ -247,10 +247,12 @@ static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { 
#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;

kernel/trace/ftrace.c

+4 −0
Original line number Diff line number Diff line
@@ -2364,6 +2364,7 @@ ftrace_find_tramp_ops_new(struct dyn_ftrace *rec) 
/* 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
@@ -5056,6 +5057,7 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr) 
		direct->addr = addr;

		direct->count = 0;

		list_add_rcu(&direct->next, &ftrace_direct_funcs);

		ftrace_direct_func_count++;

	}



	entry->ip = ip;
@@ -5081,6 +5083,7 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr) 
			if (free_hash)

				free_ftrace_hash(free_hash);

			free_hash = NULL;

			ftrace_direct_func_count--;

		}

	} else {

		if (!direct->count)
@@ -5141,6 +5144,7 @@ int unregister_ftrace_direct(unsigned long ip, unsigned long addr) 
			list_del_rcu(&direct->next);

			synchronize_rcu_tasks();

			kfree(direct);

			ftrace_direct_func_count--;

		}

	}

 out_unlock:

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