2 files changed, 14 insertions, 3 deletions

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index a71158369fd..e90e81ef6ab 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -21,6 +21,7 @@ struct task_struct;
 struct exec_domain;
 #include <asm/processor.h>
 #include <asm/ftrace.h>
+#include <asm/atomic.h>
 
 struct thread_info {
 	struct task_struct	*task;		/* main task structure */
@@ -45,6 +46,11 @@ struct thread_info {
 	int		curr_ret_stack;
 	/* Stack of return addresses for return function tracing */
 	struct ftrace_ret_stack	ret_stack[FTRACE_RET_STACK_SIZE];
+	/*
+	 * Number of functions that haven't been traced
+	 * because of depth overrun.
+	 */
+	atomic_t	trace_overrun;
 #endif
 };
 
@@ -61,6 +67,7 @@ struct thread_info {
 		.fn = do_no_restart_syscall,	\
 	},					\
 	.curr_ret_stack = -1,\
+	.trace_overrun	= ATOMIC_INIT(0)	\
 }
 #else
 #define INIT_THREAD_INFO(tsk)			\
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 924153edd97..356bb1eb6e9 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -353,8 +353,10 @@ static int push_return_trace(unsigned long ret, unsigned long long time,
 	struct thread_info *ti = current_thread_info();
 
 	/* The return trace stack is full */
-	if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1)
+	if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1) {
+		atomic_inc(&ti->trace_overrun);
 		return -EBUSY;
+	}
 
 	index = ++ti->curr_ret_stack;
 	barrier();
@@ -367,7 +369,7 @@ static int push_return_trace(unsigned long ret, unsigned long long time,
 
 /* Retrieve a function return address to the trace stack on thread info.*/
 static void pop_return_trace(unsigned long *ret, unsigned long long *time,
-				unsigned long *func)
+				unsigned long *func, unsigned long *overrun)
 {
 	int index;
 
@@ -376,6 +378,7 @@ static void pop_return_trace(unsigned long *ret, unsigned long long *time,
 	*ret = ti->ret_stack[index].ret;
 	*func = ti->ret_stack[index].func;
 	*time = ti->ret_stack[index].calltime;
+	*overrun = atomic_read(&ti->trace_overrun);
 	ti->curr_ret_stack--;
 }
 
@@ -386,7 +389,8 @@ static void pop_return_trace(unsigned long *ret, unsigned long long *time,
 unsigned long ftrace_return_to_handler(void)
 {
 	struct ftrace_retfunc trace;
-	pop_return_trace(&trace.ret, &trace.calltime, &trace.func);
+	pop_return_trace(&trace.ret, &trace.calltime, &trace.func,
+			&trace.overrun);
 	trace.rettime = cpu_clock(raw_smp_processor_id());
 	ftrace_function_return(&trace);