Merge branch 'tracing/function-return-tracer' into tracing/fastboot

16 files changed, 506 insertions, 16 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6ab097fd5241..7780cc8b51d1 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -29,6 +29,7 @@ config X86
         select HAVE_FTRACE_MCOUNT_RECORD
         select HAVE_DYNAMIC_FTRACE
         select HAVE_FUNCTION_TRACER
+        select HAVE_FUNCTION_RET_TRACER if X86_32
         select HAVE_FUNCTION_TRACE_MCOUNT_TEST
         select HAVE_KVM if ((X86_32 && !X86_VOYAGER && !X86_VISWS && !X86_NUMAQ) || X86_64)
         select HAVE_ARCH_KGDB if !X86_VOYAGER
diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index f8173ed1c970..9b6a1fa19e70 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -20,4 +20,30 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_FUNCTION_TRACER */
 
+#ifdef CONFIG_FUNCTION_RET_TRACER
+#define FTRACE_RET_STACK_SIZE 20
+
+#ifndef __ASSEMBLY__
+
+/*
+ * Stack of return addresses for functions
+ * of a thread.
+ * Used in struct thread_info
+ */
+struct ftrace_ret_stack {
+        unsigned long ret;
+        unsigned long func;
+        unsigned long long calltime;
+};
+
+/*
+ * Primary handler of a function return.
+ * It relays on ftrace_return_to_handler.
+ * Defined in entry32.S
+ */
+extern void return_to_handler(void);
+
+#endif /* __ASSEMBLY__ */
+#endif /* CONFIG_FUNCTION_RET_TRACER */
+
 #endif /* _ASM_X86_FTRACE_H */
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index e44d379faad2..a71158369fd4 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -20,6 +20,7 @@
 struct task_struct;
 struct exec_domain;
 #include <asm/processor.h>
+#include <asm/ftrace.h>
 
 struct thread_info {
         struct task_struct      *task;          /* main task structure */
@@ -38,8 +39,30 @@ struct thread_info {
                                                 */
         __u8                    supervisor_stack[0];
 #endif
+
+#ifdef CONFIG_FUNCTION_RET_TRACER
+        /* Index of current stored adress in ret_stack */
+        int             curr_ret_stack;
+        /* Stack of return addresses for return function tracing */
+        struct ftrace_ret_stack ret_stack[FTRACE_RET_STACK_SIZE];
+#endif
 };
 
+#ifdef CONFIG_FUNCTION_RET_TRACER
+#define INIT_THREAD_INFO(tsk)                   \
+{                                               \
+        .task           = &tsk,                 \
+        .exec_domain    = &default_exec_domain, \
+        .flags          = 0,                    \
+        .cpu            = 0,                    \
+        .preempt_count  = 1,                    \
+        .addr_limit     = KERNEL_DS,            \
+        .restart_block = {                      \
+                .fn = do_no_restart_syscall,    \
+        },                                      \
+        .curr_ret_stack = -1,\
+}
+#else
 #define INIT_THREAD_INFO(tsk)                   \
 {                                               \
         .task           = &tsk,                 \
@@ -52,6 +75,7 @@ struct thread_info {
                 .fn = do_no_restart_syscall,    \
         },                                      \
 }
+#endif
 
 #define init_thread_info        (init_thread_union.thread_info)
 #define init_stack              (init_thread_union.stack)
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index e489ff9cb3e2..1d8ed95da846 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -14,6 +14,11 @@ CFLAGS_REMOVE_paravirt-spinlocks.o = -pg
 CFLAGS_REMOVE_ftrace.o = -pg
 endif
 
+ifdef CONFIG_FUNCTION_RET_TRACER
+# Don't trace __switch_to() but let it for function tracer
+CFLAGS_REMOVE_process_32.o = -pg
+endif
+
 #
 # vsyscalls (which work on the user stack) should have
 # no stack-protector checks:
@@ -65,6 +70,7 @@ obj-$(CONFIG_X86_LOCAL_APIC)	+= apic.o nmi.o
 obj-$(CONFIG_X86_IO_APIC)       += io_apic.o
 obj-$(CONFIG_X86_REBOOTFIXUPS)  += reboot_fixups_32.o
 obj-$(CONFIG_DYNAMIC_FTRACE)    += ftrace.o
+obj-$(CONFIG_FUNCTION_RET_TRACER)       += ftrace.o
 obj-$(CONFIG_KEXEC)             += machine_kexec_$(BITS).o
 obj-$(CONFIG_KEXEC)             += relocate_kernel_$(BITS).o crash.o
 obj-$(CONFIG_CRASH_DUMP)        += crash_dump_$(BITS).o
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 9134de814c97..9a0ac85946db 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1188,6 +1188,10 @@ ENTRY(mcount)
 
         cmpl $ftrace_stub, ftrace_trace_function
         jnz trace
+#ifdef CONFIG_FUNCTION_RET_TRACER
+        cmpl $ftrace_stub, ftrace_function_return
+        jnz trace_return
+#endif
 .globl ftrace_stub
 ftrace_stub:
         ret
@@ -1206,8 +1210,37 @@ trace:
         popl %edx
         popl %ecx
         popl %eax
+        jmp ftrace_stub
 
+#ifdef CONFIG_FUNCTION_RET_TRACER
+trace_return:
+        pushl %eax
+        pushl %ecx
+        pushl %edx
+        movl 0xc(%esp), %eax
+        pushl %eax
+        lea 0x4(%ebp), %eax
+        pushl %eax
+        call prepare_ftrace_return
+        addl $8, %esp
+        popl %edx
+        popl %ecx
+        popl %eax
         jmp ftrace_stub
+
+.globl return_to_handler
+return_to_handler:
+        pushl $0
+        pushl %eax
+        pushl %ecx
+        pushl %edx
+        call ftrace_return_to_handler
+        movl %eax, 0xc(%esp)
+        popl %edx
+        popl %ecx
+        popl %eax
+        ret
+#endif /* CONFIG_FUNCTION_RET_TRACER */
 END(mcount)
 #endif /* CONFIG_DYNAMIC_FTRACE */
 #endif /* CONFIG_FUNCTION_TRACER */
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 69149337f2fe..16a571dea2ef 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -14,14 +14,178 @@
 #include <linux/uaccess.h>
 #include <linux/ftrace.h>
 #include <linux/percpu.h>
+#include <linux/sched.h>
 #include <linux/init.h>
 #include <linux/list.h>
 
 #include <asm/ftrace.h>
+#include <linux/ftrace.h>
 #include <asm/nops.h>
+#include <asm/nmi.h>
 
 
-static unsigned char ftrace_nop[MCOUNT_INSN_SIZE];
+
+#ifdef CONFIG_FUNCTION_RET_TRACER
+
+/*
+ * These functions are picked from those used on
+ * this page for dynamic ftrace. They have been
+ * simplified to ignore all traces in NMI context.
+ */
+static atomic_t in_nmi;
+
+void ftrace_nmi_enter(void)
+{
+        atomic_inc(&in_nmi);
+}
+
+void ftrace_nmi_exit(void)
+{
+        atomic_dec(&in_nmi);
+}
+
+/*
+ * Synchronize accesses to return adresses stack with
+ * interrupts.
+ */
+static raw_spinlock_t ret_stack_lock;
+
+/* Add a function return address to the trace stack on thread info.*/
+static int push_return_trace(unsigned long ret, unsigned long long time,
+                                unsigned long func)
+{
+        int index;
+        struct thread_info *ti;
+        unsigned long flags;
+        int err = 0;
+
+        raw_local_irq_save(flags);
+        __raw_spin_lock(&ret_stack_lock);
+
+        ti = current_thread_info();
+        /* The return trace stack is full */
+        if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1) {
+                err = -EBUSY;
+                goto out;
+        }
+
+        index = ++ti->curr_ret_stack;
+        ti->ret_stack[index].ret = ret;
+        ti->ret_stack[index].func = func;
+        ti->ret_stack[index].calltime = time;
+
+out:
+        __raw_spin_unlock(&ret_stack_lock);
+        raw_local_irq_restore(flags);
+        return err;
+}
+
+/* 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)
+{
+        struct thread_info *ti;
+        int index;
+        unsigned long flags;
+
+        raw_local_irq_save(flags);
+        __raw_spin_lock(&ret_stack_lock);
+
+        ti = current_thread_info();
+        index = ti->curr_ret_stack;
+        *ret = ti->ret_stack[index].ret;
+        *func = ti->ret_stack[index].func;
+        *time = ti->ret_stack[index].calltime;
+        ti->curr_ret_stack--;
+
+        __raw_spin_unlock(&ret_stack_lock);
+        raw_local_irq_restore(flags);
+}
+
+/*
+ * Send the trace to the ring-buffer.
+ * @return the original return address.
+ */
+unsigned long ftrace_return_to_handler(void)
+{
+        struct ftrace_retfunc trace;
+        pop_return_trace(&trace.ret, &trace.calltime, &trace.func);
+        trace.rettime = cpu_clock(raw_smp_processor_id());
+        ftrace_function_return(&trace);
+
+        return trace.ret;
+}
+
+/*
+ * Hook the return address and push it in the stack of return addrs
+ * in current thread info.
+ */
+asmlinkage
+void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
+{
+        unsigned long old;
+        unsigned long long calltime;
+        int faulted;
+        unsigned long return_hooker = (unsigned long)
+                                &return_to_handler;
+
+        /* Nmi's are currently unsupported */
+        if (atomic_read(&in_nmi))
+                return;
+
+        /*
+         * Protect against fault, even if it shouldn't
+         * happen. This tool is too much intrusive to
+         * ignore such a protection.
+         */
+        asm volatile(
+                "1: movl (%[parent_old]), %[old]\n"
+                "2: movl %[return_hooker], (%[parent_replaced])\n"
+                "   movl $0, %[faulted]\n"
+
+                ".section .fixup, \"ax\"\n"
+                "3: movl $1, %[faulted]\n"
+                ".previous\n"
+
+                ".section __ex_table, \"a\"\n"
+                "   .long 1b, 3b\n"
+                "   .long 2b, 3b\n"
+                ".previous\n"
+
+                : [parent_replaced] "=r" (parent), [old] "=r" (old),
+                  [faulted] "=r" (faulted)
+                : [parent_old] "0" (parent), [return_hooker] "r" (return_hooker)
+                : "memory"
+        );
+
+        if (WARN_ON(faulted)) {
+                unregister_ftrace_return();
+                return;
+        }
+
+        if (WARN_ON(!__kernel_text_address(old))) {
+                unregister_ftrace_return();
+                *parent = old;
+                return;
+        }
+
+        calltime = cpu_clock(raw_smp_processor_id());
+
+        if (push_return_trace(old, calltime, self_addr) == -EBUSY)
+                *parent = old;
+}
+
+static int __init init_ftrace_function_return(void)
+{
+        ret_stack_lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
+        return 0;
+}
+device_initcall(init_ftrace_function_return);
+
+
+#endif
+
+#ifdef CONFIG_DYNAMIC_FTRACE
 
 union ftrace_code_union {
         char code[MCOUNT_INSN_SIZE];
@@ -31,17 +195,11 @@ union ftrace_code_union {
         } __attribute__((packed));
 };
 
-
 static int ftrace_calc_offset(long ip, long addr)
 {
         return (int)(addr - ip);
 }
 
-unsigned char *ftrace_nop_replace(void)
-{
-        return ftrace_nop;
-}
-
 unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
 {
         static union ftrace_code_union calc;
@@ -183,6 +341,15 @@ do_ftrace_mod_code(unsigned long ip, void *new_code)
 }
 
 
+
+
+static unsigned char ftrace_nop[MCOUNT_INSN_SIZE];
+
+unsigned char *ftrace_nop_replace(void)
+{
+        return ftrace_nop;
+}
+
 int
 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                    unsigned char *new_code)
@@ -292,3 +459,4 @@ int __init ftrace_dyn_arch_init(void *data)
 
         return 0;
 }
+#endif
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 1f5608c11023..dcbbf72a88b1 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -268,6 +268,26 @@ ftrace_init_module(unsigned long *start, unsigned long *end) { }
 
 
 /*
+ * Structure that defines a return function trace.
+ */
+struct ftrace_retfunc {
+        unsigned long ret; /* Return address */
+        unsigned long func; /* Current function */
+        unsigned long long calltime;
+        unsigned long long rettime;
+};
+
+#ifdef CONFIG_FUNCTION_RET_TRACER
+/* Type of a callback handler of tracing return function */
+typedef void (*trace_function_return_t)(struct ftrace_retfunc *);
+
+extern void register_ftrace_return(trace_function_return_t func);
+/* The current handler in use */
+extern trace_function_return_t ftrace_function_return;
+extern void unregister_ftrace_return(void);
+#endif
+
+/*
  * Structure which defines the trace of an initcall.
  * You don't have to fill the func field since it is
  * only used internally by the tracer.
diff --git a/include/linux/ftrace_irq.h b/include/linux/ftrace_irq.h
index b1299d6729f2..0b4df55d7a74 100644
--- a/include/linux/ftrace_irq.h
+++ b/include/linux/ftrace_irq.h
@@ -2,7 +2,7 @@
 #define _LINUX_FTRACE_IRQ_H
 
 
-#ifdef CONFIG_DYNAMIC_FTRACE
+#if defined(CONFIG_DYNAMIC_FTRACE) || defined(CONFIG_FUNCTION_RET_TRACER)
 extern void ftrace_nmi_enter(void);
 extern void ftrace_nmi_exit(void);
 #else
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 644ffbda17ca..61c8cc36028a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2006,6 +2006,17 @@ static inline void setup_thread_stack(struct task_struct *p, struct task_struct
 {
         *task_thread_info(p) = *task_thread_info(org);
         task_thread_info(p)->task = p;
+
+#ifdef CONFIG_FUNCTION_RET_TRACER
+        /*
+         * When fork() creates a child process, this function is called.
+         * But the child task may not inherit the return adresses traced
+         * by the return function tracer because it will directly execute
+         * in userspace and will not return to kernel functions its parent
+         * used.
+         */
+        task_thread_info(p)->curr_ret_stack = -1;
+#endif
 }
 
 static inline unsigned long *end_of_stack(struct task_struct *p)
diff --git a/kernel/Makefile b/kernel/Makefile
index 9a3ec66a9d84..af3be57acbbb 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -23,6 +23,10 @@ CFLAGS_REMOVE_cgroup-debug.o = -pg
 CFLAGS_REMOVE_sched_clock.o = -pg
 CFLAGS_REMOVE_sched.o = -mno-spe -pg
 endif
+ifdef CONFIG_FUNCTION_RET_TRACER
+CFLAGS_REMOVE_extable.o = -pg # For __kernel_text_address()
+CFLAGS_REMOVE_module.o = -pg # For __module_text_address()
+endif
 
 obj-$(CONFIG_FREEZER) += freezer.o
 obj-$(CONFIG_PROFILING) += profile.o
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index fc4febc3334a..d986216c8327 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -9,6 +9,9 @@ config NOP_TRACER
 config HAVE_FUNCTION_TRACER
         bool
 
+config HAVE_FUNCTION_RET_TRACER
+        bool
+
 config HAVE_FUNCTION_TRACE_MCOUNT_TEST
         bool
         help
@@ -54,6 +57,17 @@ config FUNCTION_TRACER
           (the bootup default), then the overhead of the instructions is very
           small and not measurable even in micro-benchmarks.
 
+config FUNCTION_RET_TRACER
+        bool "Kernel Function return Tracer"
+        depends on !DYNAMIC_FTRACE
+        depends on HAVE_FUNCTION_RET_TRACER
+        depends on FUNCTION_TRACER
+        help
+          Enable the kernel to trace a function at its return.
+          It's first purpose is to trace the duration of functions.
+          This is done by setting the current return address on the thread
+          info structure of the current task.
+
 config IRQSOFF_TRACER
         bool "Interrupts-off Latency Tracer"
         default n
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index c8228b1a49e9..3e1f361bbc17 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -24,5 +24,6 @@ obj-$(CONFIG_NOP_TRACER) += trace_nop.o
 obj-$(CONFIG_STACK_TRACER) += trace_stack.o
 obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
 obj-$(CONFIG_BOOT_TRACER) += trace_boot.o
+obj-$(CONFIG_FUNCTION_RET_TRACER) += trace_functions_return.o
 
 libftrace-y := ftrace.o
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 25b803559f17..beb21a51e1ef 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1480,3 +1480,19 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
         return ret;
 }
 
+#ifdef CONFIG_FUNCTION_RET_TRACER
+trace_function_return_t ftrace_function_return =
+                        (trace_function_return_t)ftrace_stub;
+void register_ftrace_return(trace_function_return_t func)
+{
+        ftrace_function_return = func;
+}
+
+void unregister_ftrace_return(void)
+{
+        ftrace_function_return = (trace_function_return_t)ftrace_stub;
+}
+#endif
+
+
+
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 216bbe7547a4..a3f7ae9cd8e1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -244,13 +244,6 @@ unsigned long nsecs_to_usecs(unsigned long nsecs)
         return nsecs / 1000;
 }
 
-/*
- * TRACE_ITER_SYM_MASK masks the options in trace_flags that
- * control the output of kernel symbols.
- */
-#define TRACE_ITER_SYM_MASK \
-        (TRACE_ITER_PRINT_PARENT|TRACE_ITER_SYM_OFFSET|TRACE_ITER_SYM_ADDR)
-
 /* These must match the bit postions in trace_iterator_flags */
 static const char *trace_options[] = {
         "print-parent",
@@ -810,6 +803,35 @@ trace_function(struct trace_array *tr, struct trace_array_cpu *data,
         ring_buffer_unlock_commit(tr->buffer, event, irq_flags);
 }
 
+#ifdef CONFIG_FUNCTION_RET_TRACER
+static void __trace_function_return(struct trace_array *tr,
+                                struct trace_array_cpu *data,
+                                struct ftrace_retfunc *trace,
+                                unsigned long flags,
+                                int pc)
+{
+        struct ring_buffer_event *event;
+        struct ftrace_ret_entry *entry;
+        unsigned long irq_flags;
+
+        if (unlikely(local_read(&__get_cpu_var(ftrace_cpu_disabled))))
+                return;
+
+        event = ring_buffer_lock_reserve(global_trace.buffer, sizeof(*entry),
+                                         &irq_flags);
+        if (!event)
+                return;
+        entry   = ring_buffer_event_data(event);
+        tracing_generic_entry_update(&entry->ent, flags, pc);
+        entry->ent.type                 = TRACE_FN_RET;
+        entry->ip                       = trace->func;
+        entry->parent_ip        = trace->ret;
+        entry->rettime          = trace->rettime;
+        entry->calltime         = trace->calltime;
+        ring_buffer_unlock_commit(global_trace.buffer, event, irq_flags);
+}
+#endif
+
 void
 ftrace(struct trace_array *tr, struct trace_array_cpu *data,
        unsigned long ip, unsigned long parent_ip, unsigned long flags,
@@ -1038,6 +1060,29 @@ function_trace_call(unsigned long ip, unsigned long parent_ip)
         raw_local_irq_restore(flags);
 }
 
+#ifdef CONFIG_FUNCTION_RET_TRACER
+void trace_function_return(struct ftrace_retfunc *trace)
+{
+        struct trace_array *tr = &global_trace;
+        struct trace_array_cpu *data;
+        unsigned long flags;
+        long disabled;
+        int cpu;
+        int pc;
+
+        raw_local_irq_save(flags);
+        cpu = raw_smp_processor_id();
+        data = tr->data[cpu];
+        disabled = atomic_inc_return(&data->disabled);
+        if (likely(disabled == 1)) {
+                pc = preempt_count();
+                __trace_function_return(tr, data, trace, flags, pc);
+        }
+        atomic_dec(&data->disabled);
+        raw_local_irq_restore(flags);
+}
+#endif /* CONFIG_FUNCTION_RET_TRACER */
+
 static struct ftrace_ops trace_ops __read_mostly =
 {
         .func = function_trace_call,
@@ -1285,7 +1330,7 @@ seq_print_sym_offset(struct trace_seq *s, const char *fmt,
 # define IP_FMT "%016lx"
 #endif
 
-static int
+int
 seq_print_ip_sym(struct trace_seq *s, unsigned long ip, unsigned long sym_flags)
 {
         int ret;
@@ -1738,6 +1783,10 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
                         trace_seq_print_cont(s, iter);
                 break;
         }
+        case TRACE_FN_RET: {
+                return print_return_function(iter);
+                break;
+        }
         }
         return TRACE_TYPE_HANDLED;
 }
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 978145088fb8..e40ce0c14690 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -22,6 +22,7 @@ enum trace_type {
         TRACE_MMIO_RW,
         TRACE_MMIO_MAP,
         TRACE_BOOT,
+        TRACE_FN_RET,
 
         __TRACE_LAST_TYPE
 };
@@ -48,6 +49,15 @@ struct ftrace_entry {
         unsigned long           ip;
         unsigned long           parent_ip;
 };
+
+/* Function return entry */
+struct ftrace_ret_entry {
+        struct trace_entry      ent;
+        unsigned long           ip;
+        unsigned long           parent_ip;
+        unsigned long long      calltime;
+        unsigned long long      rettime;
+};
 extern struct tracer boot_tracer;
 
 /*
@@ -218,6 +228,7 @@ extern void __ftrace_bad_type(void);
                 IF_ASSIGN(var, ent, struct trace_mmiotrace_map,         \
                           TRACE_MMIO_MAP);                              \
                 IF_ASSIGN(var, ent, struct trace_boot, TRACE_BOOT);     \
+                IF_ASSIGN(var, ent, struct ftrace_ret_entry, TRACE_FN_RET); \
                 __ftrace_bad_type();                                    \
         } while (0)
 
@@ -321,6 +332,8 @@ void trace_function(struct trace_array *tr,
                     unsigned long ip,
                     unsigned long parent_ip,
                     unsigned long flags, int pc);
+void
+trace_function_return(struct ftrace_retfunc *trace);
 
 void tracing_start_cmdline_record(void);
 void tracing_stop_cmdline_record(void);
@@ -393,6 +406,10 @@ extern void *head_page(struct trace_array_cpu *data);
 extern int trace_seq_printf(struct trace_seq *s, const char *fmt, ...);
 extern void trace_seq_print_cont(struct trace_seq *s,
                                  struct trace_iterator *iter);
+
+extern int
+seq_print_ip_sym(struct trace_seq *s, unsigned long ip,
+                unsigned long sym_flags);
 extern ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
                                  size_t cnt);
 extern long ns2usecs(cycle_t nsec);
@@ -400,6 +417,17 @@ extern int trace_vprintk(unsigned long ip, const char *fmt, va_list args);
 
 extern unsigned long trace_flags;
 
+/* Standard output formatting function used for function return traces */
+#ifdef CONFIG_FUNCTION_RET_TRACER
+extern enum print_line_t print_return_function(struct trace_iterator *iter);
+#else
+static inline enum print_line_t
+print_return_function(struct trace_iterator *iter)
+{
+        return TRACE_TYPE_UNHANDLED;
+}
+#endif
+
 /*
  * trace_iterator_flags is an enumeration that defines bit
  * positions into trace_flags that controls the output.
@@ -422,6 +450,13 @@ enum trace_iterator_flags {
         TRACE_ITER_PREEMPTONLY          = 0x800,
 };
 
+/*
+ * TRACE_ITER_SYM_MASK masks the options in trace_flags that
+ * control the output of kernel symbols.
+ */
+#define TRACE_ITER_SYM_MASK \
+        (TRACE_ITER_PRINT_PARENT|TRACE_ITER_SYM_OFFSET|TRACE_ITER_SYM_ADDR)
+
 extern struct tracer nop_trace;
 
 /**
diff --git a/kernel/trace/trace_functions_return.c b/kernel/trace/trace_functions_return.c
new file mode 100644
index 000000000000..7680b21537dd
--- /dev/null
+++ b/kernel/trace/trace_functions_return.c
@@ -0,0 +1,82 @@
+/*
+ *
+ * Function return tracer.
+ * Copyright (c) 2008 Frederic Weisbecker <fweisbec@gmail.com>
+ * Mostly borrowed from function tracer which
+ * is Copyright (c) Steven Rostedt <srostedt@redhat.com>
+ *
+ */
+#include <linux/debugfs.h>
+#include <linux/uaccess.h>
+#include <linux/ftrace.h>
+#include <linux/fs.h>
+
+#include "trace.h"
+
+
+static void start_return_trace(struct trace_array *tr)
+{
+        register_ftrace_return(&trace_function_return);
+}
+
+static void stop_return_trace(struct trace_array *tr)
+{
+        unregister_ftrace_return();
+}
+
+static void return_trace_init(struct trace_array *tr)
+{
+        int cpu;
+        for_each_online_cpu(cpu)
+                tracing_reset(tr, cpu);
+
+        start_return_trace(tr);
+}
+
+static void return_trace_reset(struct trace_array *tr)
+{
+                stop_return_trace(tr);
+}
+
+
+enum print_line_t
+print_return_function(struct trace_iterator *iter)
+{
+        struct trace_seq *s = &iter->seq;
+        struct trace_entry *entry = iter->ent;
+        struct ftrace_ret_entry *field;
+        int ret;
+
+        if (entry->type == TRACE_FN_RET) {
+                trace_assign_type(field, entry);
+                ret = trace_seq_printf(s, "%pF -> ", (void *)field->parent_ip);
+                if (!ret)
+                        return TRACE_TYPE_PARTIAL_LINE;
+                ret = seq_print_ip_sym(s, field->ip,
+                                        trace_flags & TRACE_ITER_SYM_MASK);
+                if (!ret)
+                        return TRACE_TYPE_PARTIAL_LINE;
+                ret = trace_seq_printf(s, " (%llu ns)\n",
+                                        field->rettime - field->calltime);
+                if (!ret)
+                        return TRACE_TYPE_PARTIAL_LINE;
+                else
+                        return TRACE_TYPE_HANDLED;
+        }
+        return TRACE_TYPE_UNHANDLED;
+}
+
+static struct tracer return_trace __read_mostly =
+{
+        .name        = "return",
+        .init        = return_trace_init,
+        .reset       = return_trace_reset,
+        .print_line = print_return_function
+};
+
+static __init int init_return_trace(void)
+{
+        return register_tracer(&return_trace);
+}
+
+device_initcall(init_return_trace);