ftrace: add quick function trace stop
Impact: quick start and stop of function tracer
This patch adds a way to disable the function tracer quickly without
the need to run kstop_machine. It adds a new variable called
function_trace_stop which will stop the calls to functions from mcount
when set. This is just an on/off switch and does not handle recursion
like preempt_disable().
It's main purpose is to help other tracers/debuggers start and stop tracing
fuctions without the need to call kstop_machine.
The config option HAVE_FUNCTION_TRACE_MCOUNT_TEST is added for archs
that implement the testing of the function_trace_stop in the mcount
arch dependent code. Otherwise, the test is done in the C code.
x86 is the only arch at the moment that supports this.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4a39d24..896c71f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -47,6 +47,9 @@
int ftrace_enabled __read_mostly;
static int last_ftrace_enabled;
+/* Quick disabling of function tracer. */
+int function_trace_stop;
+
/*
* ftrace_disabled is set when an anomaly is discovered.
* ftrace_disabled is much stronger than ftrace_enabled.
@@ -63,6 +66,7 @@
static struct ftrace_ops *ftrace_list __read_mostly = &ftrace_list_end;
ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
+ftrace_func_t __ftrace_trace_function __read_mostly = ftrace_stub;
static void ftrace_list_func(unsigned long ip, unsigned long parent_ip)
{
@@ -88,8 +92,23 @@
void clear_ftrace_function(void)
{
ftrace_trace_function = ftrace_stub;
+ __ftrace_trace_function = ftrace_stub;
}
+#ifndef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
+/*
+ * For those archs that do not test ftrace_trace_stop in their
+ * mcount call site, we need to do it from C.
+ */
+static void ftrace_test_stop_func(unsigned long ip, unsigned long parent_ip)
+{
+ if (function_trace_stop)
+ return;
+
+ __ftrace_trace_function(ip, parent_ip);
+}
+#endif
+
static int __register_ftrace_function(struct ftrace_ops *ops)
{
/* should not be called from interrupt context */
@@ -110,10 +129,18 @@
* For one func, simply call it directly.
* For more than one func, call the chain.
*/
+#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
if (ops->next == &ftrace_list_end)
ftrace_trace_function = ops->func;
else
ftrace_trace_function = ftrace_list_func;
+#else
+ if (ops->next == &ftrace_list_end)
+ __ftrace_trace_function = ops->func;
+ else
+ __ftrace_trace_function = ftrace_list_func;
+ ftrace_trace_function = ftrace_test_stop_func;
+#endif
}
spin_unlock(&ftrace_lock);
@@ -526,7 +553,7 @@
}
static ftrace_func_t saved_ftrace_func;
-static int ftrace_start;
+static int ftrace_start_up;
static DEFINE_MUTEX(ftrace_start_lock);
static void ftrace_startup(void)
@@ -537,8 +564,8 @@
return;
mutex_lock(&ftrace_start_lock);
- ftrace_start++;
- if (ftrace_start == 1)
+ ftrace_start_up++;
+ if (ftrace_start_up == 1)
command |= FTRACE_ENABLE_CALLS;
if (saved_ftrace_func != ftrace_trace_function) {
@@ -562,8 +589,8 @@
return;
mutex_lock(&ftrace_start_lock);
- ftrace_start--;
- if (!ftrace_start)
+ ftrace_start_up--;
+ if (!ftrace_start_up)
command |= FTRACE_DISABLE_CALLS;
if (saved_ftrace_func != ftrace_trace_function) {
@@ -589,8 +616,8 @@
mutex_lock(&ftrace_start_lock);
/* Force update next time */
saved_ftrace_func = NULL;
- /* ftrace_start is true if we want ftrace running */
- if (ftrace_start)
+ /* ftrace_start_up is true if we want ftrace running */
+ if (ftrace_start_up)
command |= FTRACE_ENABLE_CALLS;
ftrace_run_update_code(command);
@@ -605,8 +632,8 @@
return;
mutex_lock(&ftrace_start_lock);
- /* ftrace_start is true if ftrace is running */
- if (ftrace_start)
+ /* ftrace_start_up is true if ftrace is running */
+ if (ftrace_start_up)
command |= FTRACE_DISABLE_CALLS;
ftrace_run_update_code(command);
@@ -1186,7 +1213,7 @@
mutex_lock(&ftrace_sysctl_lock);
mutex_lock(&ftrace_start_lock);
- if (iter->filtered && ftrace_start && ftrace_enabled)
+ if (iter->filtered && ftrace_start_up && ftrace_enabled)
ftrace_run_update_code(FTRACE_ENABLE_CALLS);
mutex_unlock(&ftrace_start_lock);
mutex_unlock(&ftrace_sysctl_lock);