ftrace: add ftrace_graph_stop() (14a866c5) · Commits · 戴 / test

Impact: new ftrace_graph_stop function While developing more features of function graph, I hit a bug that caused the WARN_ON to trigger in the prepare_ftrace_return function. Well, it was hard for me to find out that was happening because the bug would not print, it would just cause a hard lockup or reboot. The reason is that it is not safe to call printk from this function. Looking further, I also found that it calls unregister_ftrace_graph, which grabs a mutex and calls kstop machine. This would definitely lock the box up if it were to trigger. This patch adds a fast and safe ftrace_graph_stop() which will stop the function tracer. Then it is safe to call the WARN ON. Signed-off-by:

Steven Rostedt <srostedt@redhat.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/ftrace.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -484,14 +484,16 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
		: "memory"
		);

		if (WARN_ON(faulted)) {
		unregister_ftrace_graph();
		if (unlikely(faulted)) {
		ftrace_graph_stop();
		WARN_ON(1);
		return;
		}

		if (WARN_ON(!__kernel_text_address(old))) {
		unregister_ftrace_graph();
		if (unlikely(!__kernel_text_address(old))) {
		ftrace_graph_stop();
		*parent = old;
		WARN_ON(1);
		return;
		}

include/linux/ftrace.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -376,6 +376,8 @@ typedef void (trace_func_graph_ent_t)(struct ftrace_graph_ent ); /* entry */
		extern int register_ftrace_graph(trace_func_graph_ret_t retfunc,
		trace_func_graph_ent_t entryfunc);

		extern void ftrace_graph_stop(void);

		/* The current handlers in use */
		extern trace_func_graph_ret_t ftrace_graph_return;
		extern trace_func_graph_ent_t ftrace_graph_entry;

kernel/trace/ftrace.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -1769,5 +1769,10 @@ void ftrace_graph_exit_task(struct task_struct *t)

		kfree(ret_stack);
		}

		void ftrace_graph_stop(void)
		{
		ftrace_stop();
		}
		#endif

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