Merge branch 'perf/urgent' into perf/core

Merge reason: Pick up pending fixes before applying dependent new changes.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

13 files changed, 194 insertions, 88 deletions

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index bcddac61422c..de6569c04cd0 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1154,7 +1154,7 @@ static int x86_pmu_handle_irq(struct pt_regs *regs)
                 /*
                  * event overflow
                  */
-                handled         = 1;
+                handled++;
                 data.period     = event->hw.last_period;
 
                 if (!x86_perf_event_set_period(event))
@@ -1200,12 +1200,20 @@ void perf_events_lapic_init(void)
         apic_write(APIC_LVTPC, APIC_DM_NMI);
 }
 
+struct pmu_nmi_state {
+        unsigned int    marked;
+        int             handled;
+};
+
+static DEFINE_PER_CPU(struct pmu_nmi_state, pmu_nmi);
+
 static int __kprobes
 perf_event_nmi_handler(struct notifier_block *self,
                          unsigned long cmd, void *__args)
 {
         struct die_args *args = __args;
-        struct pt_regs *regs;
+        unsigned int this_nmi;
+        int handled;
 
         if (!atomic_read(&active_events))
                 return NOTIFY_DONE;
@@ -1214,22 +1222,47 @@ perf_event_nmi_handler(struct notifier_block *self,
         case DIE_NMI:
         case DIE_NMI_IPI:
                 break;
-
+        case DIE_NMIUNKNOWN:
+                this_nmi = percpu_read(irq_stat.__nmi_count);
+                if (this_nmi != __get_cpu_var(pmu_nmi).marked)
+                        /* let the kernel handle the unknown nmi */
+                        return NOTIFY_DONE;
+                /*
+                 * This one is a PMU back-to-back nmi. Two events
+                 * trigger 'simultaneously' raising two back-to-back
+                 * NMIs. If the first NMI handles both, the latter
+                 * will be empty and daze the CPU. So, we drop it to
+                 * avoid false-positive 'unknown nmi' messages.
+                 */
+                return NOTIFY_STOP;
         default:
                 return NOTIFY_DONE;
         }
 
-        regs = args->regs;
-
         apic_write(APIC_LVTPC, APIC_DM_NMI);
-        /*
-         * Can't rely on the handled return value to say it was our NMI, two
-         * events could trigger 'simultaneously' raising two back-to-back NMIs.
-         *
-         * If the first NMI handles both, the latter will be empty and daze
-         * the CPU.
-         */
-        x86_pmu.handle_irq(regs);
+
+        handled = x86_pmu.handle_irq(args->regs);
+        if (!handled)
+                return NOTIFY_DONE;
+
+        this_nmi = percpu_read(irq_stat.__nmi_count);
+        if ((handled > 1) ||
+                /* the next nmi could be a back-to-back nmi */
+            ((__get_cpu_var(pmu_nmi).marked == this_nmi) &&
+             (__get_cpu_var(pmu_nmi).handled > 1))) {
+                /*
+                 * We could have two subsequent back-to-back nmis: The
+                 * first handles more than one counter, the 2nd
+                 * handles only one counter and the 3rd handles no
+                 * counter.
+                 *
+                 * This is the 2nd nmi because the previous was
+                 * handling more than one counter. We will mark the
+                 * next (3rd) and then drop it if unhandled.
+                 */
+                __get_cpu_var(pmu_nmi).marked   = this_nmi + 1;
+                __get_cpu_var(pmu_nmi).handled  = handled;
+        }
 
         return NOTIFY_STOP;
 }
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index d8d86d014008..ee05c90012d2 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -712,7 +712,8 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
         struct perf_sample_data data;
         struct cpu_hw_events *cpuc;
         int bit, loops;
-        u64 ack, status;
+        u64 status;
+        int handled = 0;
 
         perf_sample_data_init(&data, 0);
 
@@ -728,6 +729,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
 
         loops = 0;
 again:
+        intel_pmu_ack_status(status);
         if (++loops > 100) {
                 WARN_ONCE(1, "perfevents: irq loop stuck!\n");
                 perf_event_print_debug();
@@ -736,19 +738,22 @@ again:
         }
 
         inc_irq_stat(apic_perf_irqs);
-        ack = status;
 
         intel_pmu_lbr_read();
 
         /*
          * PEBS overflow sets bit 62 in the global status register
          */
-        if (__test_and_clear_bit(62, (unsigned long *)&status))
+        if (__test_and_clear_bit(62, (unsigned long *)&status)) {
+                handled++;
                 x86_pmu.drain_pebs(regs);
+        }
 
         for_each_set_bit(bit, (unsigned long *)&status, X86_PMC_IDX_MAX) {
                 struct perf_event *event = cpuc->events[bit];
 
+                handled++;
+
                 if (!test_bit(bit, cpuc->active_mask))
                         continue;
 
@@ -761,8 +766,6 @@ again:
                         x86_pmu_stop(event);
         }
 
-        intel_pmu_ack_status(ack);
-
         /*
          * Repeat if there is more work to be done:
          */
@@ -772,7 +775,7 @@ again:
 
 done:
         intel_pmu_enable_all(0);
-        return 1;
+        return handled;
 }
 
 static struct event_constraint *
diff --git a/arch/x86/kernel/cpu/perf_event_p4.c b/arch/x86/kernel/cpu/perf_event_p4.c
index 4fe62c7165c8..c70c878ee02a 100644
--- a/arch/x86/kernel/cpu/perf_event_p4.c
+++ b/arch/x86/kernel/cpu/perf_event_p4.c
@@ -936,7 +936,7 @@ static int p4_pmu_handle_irq(struct pt_regs *regs)
                 inc_irq_stat(apic_perf_irqs);
         }
 
-        return handled > 0;
+        return handled;
 }
 
 /*
diff --git a/arch/x86/oprofile/nmi_int.c b/arch/x86/oprofile/nmi_int.c
index f6b48f6c5951..cfe4faabb0f6 100644
--- a/arch/x86/oprofile/nmi_int.c
+++ b/arch/x86/oprofile/nmi_int.c
@@ -568,8 +568,13 @@ static int __init init_sysfs(void)
         int error;
 
         error = sysdev_class_register(&oprofile_sysclass);
-        if (!error)
-                error = sysdev_register(&device_oprofile);
+        if (error)
+                return error;
+
+        error = sysdev_register(&device_oprofile);
+        if (error)
+                sysdev_class_unregister(&oprofile_sysclass);
+
         return error;
 }
 
@@ -580,8 +585,10 @@ static void exit_sysfs(void)
 }
 
 #else
-#define init_sysfs() do { } while (0)
-#define exit_sysfs() do { } while (0)
+
+static inline int  init_sysfs(void) { return 0; }
+static inline void exit_sysfs(void) { }
+
 #endif /* CONFIG_PM */
 
 static int __init p4_init(char **cpu_type)
@@ -695,6 +702,8 @@ int __init op_nmi_init(struct oprofile_operations *ops)
         char *cpu_type = NULL;
         int ret = 0;
 
+        using_nmi = 0;
+
         if (!cpu_has_apic)
                 return -ENODEV;
 
@@ -774,7 +783,10 @@ int __init op_nmi_init(struct oprofile_operations *ops)
 
         mux_init(ops);
 
-        init_sysfs();
+        ret = init_sysfs();
+        if (ret)
+                return ret;
+
         using_nmi = 1;
         printk(KERN_INFO "oprofile: using NMI interrupt.\n");
         return 0;
diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c
index a9352b2c7ac4..b7e755f4178a 100644
--- a/drivers/oprofile/buffer_sync.c
+++ b/drivers/oprofile/buffer_sync.c
@@ -141,16 +141,6 @@ static struct notifier_block module_load_nb = {
         .notifier_call = module_load_notify,
 };
 
-
-static void end_sync(void)
-{
-        end_cpu_work();
-        /* make sure we don't leak task structs */
-        process_task_mortuary();
-        process_task_mortuary();
-}
-
-
 int sync_start(void)
 {
         int err;
@@ -158,7 +148,7 @@ int sync_start(void)
         if (!zalloc_cpumask_var(&marked_cpus, GFP_KERNEL))
                 return -ENOMEM;
 
-        start_cpu_work();
+        mutex_lock(&buffer_mutex);
 
         err = task_handoff_register(&task_free_nb);
         if (err)
@@ -173,7 +163,10 @@ int sync_start(void)
         if (err)
                 goto out4;
 
+        start_cpu_work();
+
 out:
+        mutex_unlock(&buffer_mutex);
         return err;
 out4:
         profile_event_unregister(PROFILE_MUNMAP, &munmap_nb);
@@ -182,7 +175,6 @@ out3:
 out2:
         task_handoff_unregister(&task_free_nb);
 out1:
-        end_sync();
         free_cpumask_var(marked_cpus);
         goto out;
 }
@@ -190,11 +182,20 @@ out1:
 
 void sync_stop(void)
 {
+        /* flush buffers */
+        mutex_lock(&buffer_mutex);
+        end_cpu_work();
         unregister_module_notifier(&module_load_nb);
         profile_event_unregister(PROFILE_MUNMAP, &munmap_nb);
         profile_event_unregister(PROFILE_TASK_EXIT, &task_exit_nb);
         task_handoff_unregister(&task_free_nb);
-        end_sync();
+        mutex_unlock(&buffer_mutex);
+        flush_scheduled_work();
+
+        /* make sure we don't leak task structs */
+        process_task_mortuary();
+        process_task_mortuary();
+
         free_cpumask_var(marked_cpus);
 }
 
diff --git a/drivers/oprofile/cpu_buffer.c b/drivers/oprofile/cpu_buffer.c
index 219f79e2210a..f179ac2ea801 100644
--- a/drivers/oprofile/cpu_buffer.c
+++ b/drivers/oprofile/cpu_buffer.c
@@ -120,8 +120,6 @@ void end_cpu_work(void)
 
                 cancel_delayed_work(&b->work);
         }
-
-        flush_scheduled_work();
 }
 
 /*
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 0d38f27ad885..2d74f31220ad 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -402,11 +402,31 @@ static void perf_group_detach(struct perf_event *event)
         }
 }
 
+static inline int
+event_filter_match(struct perf_event *event)
+{
+        return event->cpu == -1 || event->cpu == smp_processor_id();
+}
+
 static void
 event_sched_out(struct perf_event *event,
                   struct perf_cpu_context *cpuctx,
                   struct perf_event_context *ctx)
 {
+        u64 delta;
+        /*
+         * An event which could not be activated because of
+         * filter mismatch still needs to have its timings
+         * maintained, otherwise bogus information is return
+         * via read() for time_enabled, time_running:
+         */
+        if (event->state == PERF_EVENT_STATE_INACTIVE
+            && !event_filter_match(event)) {
+                delta = ctx->time - event->tstamp_stopped;
+                event->tstamp_running += delta;
+                event->tstamp_stopped = ctx->time;
+        }
+
         if (event->state != PERF_EVENT_STATE_ACTIVE)
                 return;
 
@@ -432,9 +452,7 @@ group_sched_out(struct perf_event *group_event,
                 struct perf_event_context *ctx)
 {
         struct perf_event *event;
-
-        if (group_event->state != PERF_EVENT_STATE_ACTIVE)
-                return;
+        int state = group_event->state;
 
         event_sched_out(group_event, cpuctx, ctx);
 
@@ -444,7 +462,7 @@ group_sched_out(struct perf_event *group_event,
         list_for_each_entry(event, &group_event->sibling_list, group_entry)
                 event_sched_out(event, cpuctx, ctx);
 
-        if (group_event->attr.exclusive)
+        if (state == PERF_EVENT_STATE_ACTIVE && group_event->attr.exclusive)
                 cpuctx->exclusive = 0;
 }
 
@@ -5942,15 +5960,15 @@ perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
 {
         unsigned int cpu = (long)hcpu;
 
-        switch (action) {
+        switch (action & ~CPU_TASKS_FROZEN) {
 
         case CPU_UP_PREPARE:
-        case CPU_UP_PREPARE_FROZEN:
+        case CPU_DOWN_FAILED:
                 perf_event_init_cpu(cpu);
                 break;
 
+        case CPU_UP_CANCELED:
         case CPU_DOWN_PREPARE:
-        case CPU_DOWN_PREPARE_FROZEN:
                 perf_event_exit_cpu(cpu);
                 break;
 
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 0d88ce9b9fb8..83a16e9ee518 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -381,12 +381,19 @@ static int function_stat_show(struct seq_file *m, void *v)
 {
         struct ftrace_profile *rec = v;
         char str[KSYM_SYMBOL_LEN];
+        int ret = 0;
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-        static DEFINE_MUTEX(mutex);
         static struct trace_seq s;
         unsigned long long avg;
         unsigned long long stddev;
 #endif
+        mutex_lock(&ftrace_profile_lock);
+
+        /* we raced with function_profile_reset() */
+        if (unlikely(rec->counter == 0)) {
+                ret = -EBUSY;
+                goto out;
+        }
 
         kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
         seq_printf(m, "  %-30.30s  %10lu", str, rec->counter);
@@ -408,7 +415,6 @@ static int function_stat_show(struct seq_file *m, void *v)
                 do_div(stddev, (rec->counter - 1) * 1000);
         }
 
-        mutex_lock(&mutex);
         trace_seq_init(&s);
         trace_print_graph_duration(rec->time, &s);
         trace_seq_puts(&s, "    ");
@@ -416,11 +422,12 @@ static int function_stat_show(struct seq_file *m, void *v)
         trace_seq_puts(&s, "    ");
         trace_print_graph_duration(stddev, &s);
         trace_print_seq(m, &s);
-        mutex_unlock(&mutex);
 #endif
         seq_putc(m, '\n');
+out:
+        mutex_unlock(&ftrace_profile_lock);
 
-        return 0;
+        return ret;
 }
 
 static void ftrace_profile_reset(struct ftrace_profile_stat *stat)
@@ -2409,7 +2416,7 @@ static const struct file_operations ftrace_filter_fops = {
         .open = ftrace_filter_open,
         .read = seq_read,
         .write = ftrace_filter_write,
-        .llseek = ftrace_regex_lseek,
+        .llseek = no_llseek,
         .release = ftrace_filter_release,
 };
 
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 92f5477a006a..f3bbcd1c90c8 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -91,6 +91,8 @@ int perf_trace_init(struct perf_event *p_event)
                     tp_event->class && tp_event->class->reg &&
                     try_module_get(tp_event->mod)) {
                         ret = perf_trace_event_init(tp_event, p_event);
+                        if (ret)
+                                module_put(tp_event->mod);
                         break;
                 }
         }
@@ -147,6 +149,7 @@ void perf_trace_destroy(struct perf_event *p_event)
                 }
         }
 out:
+        module_put(tp_event->mod);
         mutex_unlock(&event_mutex);
 }
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 8b27c9849b42..544301d29dee 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -514,8 +514,8 @@ static int kprobe_dispatcher(struct kprobe *kp, struct pt_regs *regs);
 static int kretprobe_dispatcher(struct kretprobe_instance *ri,
                                 struct pt_regs *regs);
 
-/* Check the name is good for event/group */
-static int check_event_name(const char *name)
+/* Check the name is good for event/group/fields */
+static int is_good_name(const char *name)
 {
         if (!isalpha(*name) && *name != '_')
                 return 0;
@@ -557,7 +557,7 @@ static struct trace_probe *alloc_trace_probe(const char *group,
         else
                 tp->rp.kp.pre_handler = kprobe_dispatcher;
 
-        if (!event || !check_event_name(event)) {
+        if (!event || !is_good_name(event)) {
                 ret = -EINVAL;
                 goto error;
         }
@@ -567,7 +567,7 @@ static struct trace_probe *alloc_trace_probe(const char *group,
         if (!tp->call.name)
                 goto error;
 
-        if (!group || !check_event_name(group)) {
+        if (!group || !is_good_name(group)) {
                 ret = -EINVAL;
                 goto error;
         }
@@ -883,7 +883,7 @@ static int create_trace_probe(int argc, char **argv)
         int i, ret = 0;
         int is_return = 0, is_delete = 0;
         char *symbol = NULL, *event = NULL, *group = NULL;
-        char *arg, *tmp;
+        char *arg;
         unsigned long offset = 0;
         void *addr = NULL;
         char buf[MAX_EVENT_NAME_LEN];
@@ -992,26 +992,36 @@ static int create_trace_probe(int argc, char **argv)
         /* parse arguments */
         ret = 0;
         for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
+                /* Increment count for freeing args in error case */
+                tp->nr_args++;
+
                 /* Parse argument name */
                 arg = strchr(argv[i], '=');
-                if (arg)
+                if (arg) {
                         *arg++ = '\0';
-                else
+                        tp->args[i].name = kstrdup(argv[i], GFP_KERNEL);
+                } else {
                         arg = argv[i];
+                        /* If argument name is omitted, set "argN" */
+                        snprintf(buf, MAX_EVENT_NAME_LEN, "arg%d", i + 1);
+                        tp->args[i].name = kstrdup(buf, GFP_KERNEL);
+                }
 
-                tp->args[i].name = kstrdup(argv[i], GFP_KERNEL);
                 if (!tp->args[i].name) {
-                        pr_info("Failed to allocate argument%d name '%s'.\n",
-                                i, argv[i]);
+                        pr_info("Failed to allocate argument[%d] name.\n", i);
                         ret = -ENOMEM;
                         goto error;
                 }
-                tmp = strchr(tp->args[i].name, ':');
-                if (tmp)
-                        *tmp = '_';     /* convert : to _ */
+
+                if (!is_good_name(tp->args[i].name)) {
+                        pr_info("Invalid argument[%d] name: %s\n",
+                                i, tp->args[i].name);
+                        ret = -EINVAL;
+                        goto error;
+                }
 
                 if (conflict_field_name(tp->args[i].name, tp->args, i)) {
-                        pr_info("Argument%d name '%s' conflicts with "
+                        pr_info("Argument[%d] name '%s' conflicts with "
                                 "another field.\n", i, argv[i]);
                         ret = -EINVAL;
                         goto error;
@@ -1020,12 +1030,9 @@ static int create_trace_probe(int argc, char **argv)
                 /* Parse fetch argument */
                 ret = parse_probe_arg(arg, tp, &tp->args[i], is_return);
                 if (ret) {
-                        pr_info("Parse error at argument%d. (%d)\n", i, ret);
-                        kfree(tp->args[i].name);
+                        pr_info("Parse error at argument[%d]. (%d)\n", i, ret);
                         goto error;
                 }
-
-                tp->nr_args++;
         }
 
         ret = register_trace_probe(tp);
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 5b1ee4f4ca0d..fa71aebda4ff 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -121,7 +121,7 @@ static void __touch_watchdog(void)
 
 void touch_softlockup_watchdog(void)
 {
-        __get_cpu_var(watchdog_touch_ts) = 0;
+        __raw_get_cpu_var(watchdog_touch_ts) = 0;
 }
 EXPORT_SYMBOL(touch_softlockup_watchdog);
 
@@ -141,7 +141,14 @@ void touch_all_softlockup_watchdogs(void)
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 void touch_nmi_watchdog(void)
 {
-        __get_cpu_var(watchdog_nmi_touch) = true;
+        if (watchdog_enabled) {
+                unsigned cpu;
+
+                for_each_present_cpu(cpu) {
+                        if (per_cpu(watchdog_nmi_touch, cpu) != true)
+                                per_cpu(watchdog_nmi_touch, cpu) = true;
+                }
+        }
         touch_softlockup_watchdog();
 }
 EXPORT_SYMBOL(touch_nmi_watchdog);
@@ -422,6 +429,9 @@ static int watchdog_enable(int cpu)
                 wake_up_process(p);
         }
 
+        /* if any cpu succeeds, watchdog is considered enabled for the system */
+        watchdog_enabled = 1;
+
         return 0;
 }
 
@@ -444,9 +454,6 @@ static void watchdog_disable(int cpu)
                 per_cpu(softlockup_watchdog, cpu) = NULL;
                 kthread_stop(p);
         }
-
-        /* if any cpu succeeds, watchdog is considered enabled for the system */
-        watchdog_enabled = 1;
 }
 
 static void watchdog_enable_all_cpus(void)
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index e72f05c3bef0..fcc16e4349df 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -1539,6 +1539,7 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
                 goto error;
         }
         tev->point.offset = pev->point.offset;
+        tev->point.retprobe = pev->point.retprobe;
         tev->nargs = pev->nargs;
         if (tev->nargs) {
                 tev->args = zalloc(sizeof(struct probe_trace_arg)
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 525136684d4e..32b81f707ff5 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -686,6 +686,25 @@ static int find_variable(Dwarf_Die *sp_die, struct probe_finder *pf)
         char buf[32], *ptr;
         int ret, nscopes;
 
+        if (!is_c_varname(pf->pvar->var)) {
+                /* Copy raw parameters */
+                pf->tvar->value = strdup(pf->pvar->var);
+                if (pf->tvar->value == NULL)
+                        return -ENOMEM;
+                if (pf->pvar->type) {
+                        pf->tvar->type = strdup(pf->pvar->type);
+                        if (pf->tvar->type == NULL)
+                                return -ENOMEM;
+                }
+                if (pf->pvar->name) {
+                        pf->tvar->name = strdup(pf->pvar->name);
+                        if (pf->tvar->name == NULL)
+                                return -ENOMEM;
+                } else
+                        pf->tvar->name = NULL;
+                return 0;
+        }
+
         if (pf->pvar->name)
                 pf->tvar->name = strdup(pf->pvar->name);
         else {
@@ -700,19 +719,6 @@ static int find_variable(Dwarf_Die *sp_die, struct probe_finder *pf)
         if (pf->tvar->name == NULL)
                 return -ENOMEM;
 
-        if (!is_c_varname(pf->pvar->var)) {
-                /* Copy raw parameters */
-                pf->tvar->value = strdup(pf->pvar->var);
-                if (pf->tvar->value == NULL)
-                        return -ENOMEM;
-                if (pf->pvar->type) {
-                        pf->tvar->type = strdup(pf->pvar->type);
-                        if (pf->tvar->type == NULL)
-                                return -ENOMEM;
-                }
-                return 0;
-        }
-
         pr_debug("Searching '%s' variable in context.\n",
                  pf->pvar->var);
         /* Search child die for local variables and parameters. */
@@ -783,6 +789,16 @@ static int convert_probe_point(Dwarf_Die *sp_die, struct probe_finder *pf)
                 /* This function has no name. */
                 tev->point.offset = (unsigned long)pf->addr;
 
+        /* Return probe must be on the head of a subprogram */
+        if (pf->pev->point.retprobe) {
+                if (tev->point.offset != 0) {
+                        pr_warning("Return probe must be on the head of"
+                                   " a real function\n");
+                        return -EINVAL;
+                }
+                tev->point.retprobe = true;
+        }
+
         pr_debug("Probe point found: %s+%lu\n", tev->point.symbol,
                  tev->point.offset);