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Commit 6331c28c authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
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ftrace: Fix dynamic selftest failure on some archs 



Archs that do not implement CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST, will
fail the dynamic ftrace selftest.

The function tracer has a quick 'off' variable that will prevent
the call back functions from being called. This variable is called
function_trace_stop. In x86, this is implemented directly in the mcount
assembly, but for other archs, an intermediate function is used called
ftrace_test_stop_func().

In dynamic ftrace, the function pointer variable ftrace_trace_function is
used to update the caller code in the mcount caller. But for archs that
do not have CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST set, it only calls
ftrace_test_stop_func() instead, which in turn calls __ftrace_trace_function.

When more than one ftrace_ops is registered, the function it calls is
ftrace_ops_list_func(), which will iterate over all registered ftrace_ops
and call the callbacks that have their hash matching.

The issue happens when two ftrace_ops are registered for different functions
and one is then unregistered. The __ftrace_trace_function is then pointed
to the remaining ftrace_ops callback function directly. This mean it will
be called for all functions that were registered to trace by both ftrace_ops
that were registered.

This is not an issue for archs with CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST,
because the update of ftrace_trace_function doesn't happen until after all
functions have been updated, and then the mcount caller is updated. But
for those archs that do use the ftrace_test_stop_func(), the update is
immediate.

The dynamic selftest fails because it hits this situation, and the
ftrace_ops that it registers fails to only trace what it was suppose to
and instead traces all other functions.

The solution is to delay the setting of __ftrace_trace_function until
after all the functions have been updated according to the registered
ftrace_ops. Also, function_trace_stop is set during the update to prevent
function tracing from calling code that is caused by the function tracer
itself.

Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 072126f4

kernel/trace/ftrace.c

+26 −0
Original line number Diff line number Diff line
@@ -88,6 +88,7 @@ static struct ftrace_ops ftrace_list_end __read_mostly = { 
static struct ftrace_ops *ftrace_global_list __read_mostly = &ftrace_list_end;

static struct ftrace_ops *ftrace_ops_list __read_mostly = &ftrace_list_end;

ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;

static ftrace_func_t __ftrace_trace_function_delay __read_mostly = ftrace_stub;

ftrace_func_t __ftrace_trace_function __read_mostly = ftrace_stub;

ftrace_func_t ftrace_pid_function __read_mostly = ftrace_stub;

static struct ftrace_ops global_ops;
@@ -146,9 +147,11 @@ void clear_ftrace_function(void) 
{

	ftrace_trace_function = ftrace_stub;

	__ftrace_trace_function = ftrace_stub;

	__ftrace_trace_function_delay = ftrace_stub;

	ftrace_pid_function = ftrace_stub;

}



#undef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST

#ifndef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST

/*

 * For those archs that do not test ftrace_trace_stop in their
@@ -207,8 +210,13 @@ static void update_ftrace_function(void) 


#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST

	ftrace_trace_function = func;

#else

#ifdef CONFIG_DYNAMIC_FTRACE

	/* do not update till all functions have been modified */

	__ftrace_trace_function_delay = func;

#else

	__ftrace_trace_function = func;

#endif

	ftrace_trace_function = ftrace_test_stop_func;

#endif

}
@@ -1607,6 +1615,12 @@ static int __ftrace_modify_code(void *data) 
{

	int *command = data;



	/*

	 * Do not call function tracer while we update the code.

	 * We are in stop machine, no worrying about races.

	 */

	function_trace_stop++;



	if (*command & FTRACE_ENABLE_CALLS)

		ftrace_replace_code(1);

	else if (*command & FTRACE_DISABLE_CALLS)
@@ -1620,6 +1634,18 @@ static int __ftrace_modify_code(void *data) 
	else if (*command & FTRACE_STOP_FUNC_RET)

		ftrace_disable_ftrace_graph_caller();



#ifndef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST

	/*

	 * For archs that call ftrace_test_stop_func(), we must

	 * wait till after we update all the function callers

	 * before we update the callback. This keeps different

	 * ops that record different functions from corrupting

	 * each other.

	 */

	__ftrace_trace_function = __ftrace_trace_function_delay;

#endif

	function_trace_stop--;



	return 0;

}