ftrace: Fix a slight race in modifying what function callback gets traced (59338f75) · Commits · 戴 / test

There's a slight race when going from a list function to a non list function. That is, when only one callback is registered to the function tracer, it gets called directly by the mcount trampoline. But if this function has filters, it may be called by the wrong functions. As the list ops callback that handles multiple callbacks that are registered to ftrace, it also handles what functions they call. While the transaction is taking place, use the list function always, and after all the updates are finished (only the functions that should be traced are being traced), then we can update the trampoline to call the function directly. Signed-off-by:

Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ftrace.c

+16 −1

Original line number	Diff line number	Diff line
		@@ -1978,12 +1978,27 @@ int __weak ftrace_arch_code_modify_post_process(void)

		void ftrace_modify_all_code(int command)
		{
		int update = command & FTRACE_UPDATE_TRACE_FUNC;

		/*
		* If the ftrace_caller calls a ftrace_ops func directly,
		* we need to make sure that it only traces functions it
		* expects to trace. When doing the switch of functions,
		* we need to update to the ftrace_ops_list_func first
		* before the transition between old and new calls are set,
		* as the ftrace_ops_list_func will check the ops hashes
		* to make sure the ops are having the right functions
		* traced.
		*/
		if (update)
		ftrace_update_ftrace_func(ftrace_ops_list_func);

		if (command & FTRACE_UPDATE_CALLS)
		ftrace_replace_code(1);
		else if (command & FTRACE_DISABLE_CALLS)
		ftrace_replace_code(0);

		if (command & FTRACE_UPDATE_TRACE_FUNC)
		if (update && ftrace_trace_function != ftrace_ops_list_func)
		ftrace_update_ftrace_func(ftrace_trace_function);

		if (command & FTRACE_START_FUNC_RET)

Admin message