tracing/function-return-tracer: support for dynamic ftrace on function return tracer
This patch adds the support for dynamic tracing on the function return tracer.
The whole difference with normal dynamic function tracing is that we don't need
to hook on a particular callback. The only pro that we want is to nop or set
dynamically the calls to ftrace_caller (which is ftrace_return_caller here).
Some security checks ensure that we are not trying to launch dynamic tracing for
return tracing while normal function tracing is already running.
An example of trace with getnstimeofday set as a filter:
ktime_get_ts+0x22/0x50 -> getnstimeofday (2283 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1396 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1825 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1426 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1464 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1524 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1434 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1464 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1502 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1404 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1397 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1051 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1314 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1344 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1163 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1390 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1374 ns)
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index b42ec1d..2f78a45 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -50,6 +50,9 @@
/* Quick disabling of function tracer. */
int function_trace_stop;
+/* By default, current tracing type is normal tracing. */
+enum ftrace_tracing_type_t ftrace_tracing_type = FTRACE_TYPE_ENTER;
+
/*
* ftrace_disabled is set when an anomaly is discovered.
* ftrace_disabled is much stronger than ftrace_enabled.
@@ -385,12 +388,21 @@
}
}
-#define FTRACE_ADDR ((long)(ftrace_caller))
static int
__ftrace_replace_code(struct dyn_ftrace *rec, int enable)
{
unsigned long ip, fl;
+ unsigned long ftrace_addr;
+
+#ifdef CONFIG_FUNCTION_RET_TRACER
+ if (ftrace_tracing_type == FTRACE_TYPE_ENTER)
+ ftrace_addr = (unsigned long)ftrace_caller;
+ else
+ ftrace_addr = (unsigned long)ftrace_return_caller;
+#else
+ ftrace_addr = (unsigned long)ftrace_caller;
+#endif
ip = rec->ip;
@@ -450,9 +462,9 @@
}
if (rec->flags & FTRACE_FL_ENABLED)
- return ftrace_make_call(rec, FTRACE_ADDR);
+ return ftrace_make_call(rec, ftrace_addr);
else
- return ftrace_make_nop(NULL, rec, FTRACE_ADDR);
+ return ftrace_make_nop(NULL, rec, ftrace_addr);
}
static void ftrace_replace_code(int enable)
@@ -1405,10 +1417,17 @@
return -1;
mutex_lock(&ftrace_sysctl_lock);
+
+ if (ftrace_tracing_type == FTRACE_TYPE_RETURN) {
+ ret = -EBUSY;
+ goto out;
+ }
+
ret = __register_ftrace_function(ops);
ftrace_startup();
- mutex_unlock(&ftrace_sysctl_lock);
+out:
+ mutex_unlock(&ftrace_sysctl_lock);
return ret;
}
@@ -1474,16 +1493,45 @@
}
#ifdef CONFIG_FUNCTION_RET_TRACER
+
+/* The callback that hooks the return of a function */
trace_function_return_t ftrace_function_return =
(trace_function_return_t)ftrace_stub;
-void register_ftrace_return(trace_function_return_t func)
+
+int register_ftrace_return(trace_function_return_t func)
{
+ int ret = 0;
+
+ mutex_lock(&ftrace_sysctl_lock);
+
+ /*
+ * Don't launch return tracing if normal function
+ * tracing is already running.
+ */
+ if (ftrace_trace_function != ftrace_stub) {
+ ret = -EBUSY;
+ goto out;
+ }
+
+ ftrace_tracing_type = FTRACE_TYPE_RETURN;
ftrace_function_return = func;
+ ftrace_startup();
+
+out:
+ mutex_unlock(&ftrace_sysctl_lock);
+ return ret;
}
void unregister_ftrace_return(void)
{
+ mutex_lock(&ftrace_sysctl_lock);
+
ftrace_function_return = (trace_function_return_t)ftrace_stub;
+ ftrace_shutdown();
+ /* Restore normal tracing type */
+ ftrace_tracing_type = FTRACE_TYPE_ENTER;
+
+ mutex_unlock(&ftrace_sysctl_lock);
}
#endif