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: Steven Rostedt <rostedt@goodmis.org>
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@ -88,6 +88,7 @@ static struct ftrace_ops ftrace_list_end __read_mostly = {
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static struct ftrace_ops *ftrace_global_list __read_mostly = &ftrace_list_end;
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static struct ftrace_ops *ftrace_ops_list __read_mostly = &ftrace_list_end;
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ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
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static ftrace_func_t __ftrace_trace_function_delay __read_mostly = ftrace_stub;
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ftrace_func_t __ftrace_trace_function __read_mostly = ftrace_stub;
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ftrace_func_t ftrace_pid_function __read_mostly = ftrace_stub;
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static struct ftrace_ops global_ops;
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@ -146,9 +147,11 @@ void clear_ftrace_function(void)
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{
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ftrace_trace_function = ftrace_stub;
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__ftrace_trace_function = ftrace_stub;
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__ftrace_trace_function_delay = ftrace_stub;
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ftrace_pid_function = ftrace_stub;
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}
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#undef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
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#ifndef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
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/*
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* For those archs that do not test ftrace_trace_stop in their
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@ -207,8 +210,13 @@ static void update_ftrace_function(void)
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#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
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ftrace_trace_function = func;
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#else
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#ifdef CONFIG_DYNAMIC_FTRACE
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/* do not update till all functions have been modified */
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__ftrace_trace_function_delay = func;
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#else
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__ftrace_trace_function = func;
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#endif
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ftrace_trace_function = ftrace_test_stop_func;
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#endif
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}
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@ -1607,6 +1615,12 @@ static int __ftrace_modify_code(void *data)
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{
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int *command = data;
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/*
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* Do not call function tracer while we update the code.
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* We are in stop machine, no worrying about races.
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*/
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function_trace_stop++;
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if (*command & FTRACE_ENABLE_CALLS)
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ftrace_replace_code(1);
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else if (*command & FTRACE_DISABLE_CALLS)
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@ -1620,6 +1634,18 @@ static int __ftrace_modify_code(void *data)
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else if (*command & FTRACE_STOP_FUNC_RET)
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ftrace_disable_ftrace_graph_caller();
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#ifndef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
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/*
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* For archs that call ftrace_test_stop_func(), we must
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* wait till after we update all the function callers
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* before we update the callback. This keeps different
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* ops that record different functions from corrupting
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* each other.
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*/
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__ftrace_trace_function = __ftrace_trace_function_delay;
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#endif
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function_trace_stop--;
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return 0;
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}
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