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-rw-r--r--kernel/trace/ftrace.c38
1 files changed, 34 insertions, 4 deletions
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 6c508ff33c62..67708f46baae 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -413,6 +413,17 @@ static int __register_ftrace_function(struct ftrace_ops *ops)
return 0;
}
+static void ftrace_sync(struct work_struct *work)
+{
+ /*
+ * This function is just a stub to implement a hard force
+ * of synchronize_sched(). This requires synchronizing
+ * tasks even in userspace and idle.
+ *
+ * Yes, function tracing is rude.
+ */
+}
+
static int __unregister_ftrace_function(struct ftrace_ops *ops)
{
int ret;
@@ -440,8 +451,12 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
* so there'll be no new users. We must ensure
* all current users are done before we free
* the control data.
+ * Note synchronize_sched() is not enough, as we
+ * use preempt_disable() to do RCU, but the function
+ * tracer can be called where RCU is not active
+ * (before user_exit()).
*/
- synchronize_sched();
+ schedule_on_each_cpu(ftrace_sync);
control_ops_free(ops);
}
} else
@@ -456,9 +471,13 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
/*
* Dynamic ops may be freed, we must make sure that all
* callers are done before leaving this function.
+ *
+ * Again, normal synchronize_sched() is not good enough.
+ * We need to do a hard force of sched synchronization.
*/
if (ops->flags & FTRACE_OPS_FL_DYNAMIC)
- synchronize_sched();
+ schedule_on_each_cpu(ftrace_sync);
+
return 0;
}
@@ -622,12 +641,18 @@ static int function_stat_show(struct seq_file *m, void *v)
if (rec->counter <= 1)
stddev = 0;
else {
- stddev = rec->time_squared - rec->counter * avg * avg;
+ /*
+ * Apply Welford's method:
+ * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)
+ */
+ stddev = rec->counter * rec->time_squared -
+ rec->time * rec->time;
+
/*
* Divide only 1000 for ns^2 -> us^2 conversion.
* trace_print_graph_duration will divide 1000 again.
*/
- do_div(stddev, (rec->counter - 1) * 1000);
+ do_div(stddev, rec->counter * (rec->counter - 1) * 1000);
}
trace_seq_init(&s);
@@ -3512,8 +3537,12 @@ EXPORT_SYMBOL_GPL(ftrace_set_global_notrace);
static char ftrace_notrace_buf[FTRACE_FILTER_SIZE] __initdata;
static char ftrace_filter_buf[FTRACE_FILTER_SIZE] __initdata;
+/* Used by function selftest to not test if filter is set */
+bool ftrace_filter_param __initdata;
+
static int __init set_ftrace_notrace(char *str)
{
+ ftrace_filter_param = true;
strlcpy(ftrace_notrace_buf, str, FTRACE_FILTER_SIZE);
return 1;
}
@@ -3521,6 +3550,7 @@ __setup("ftrace_notrace=", set_ftrace_notrace);
static int __init set_ftrace_filter(char *str)
{
+ ftrace_filter_param = true;
strlcpy(ftrace_filter_buf, str, FTRACE_FILTER_SIZE);
return 1;
}