ftrace: Fix dynamic selftest failure on some archs (6331c28c) · Commits · 戴 / test

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:

Steven Rostedt <rostedt@goodmis.org>

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;
		}

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