On Sat, 7 Dec 2024 09:47:10 -0500
Steven Rostedt [off-list ref] wrote:

On Sat, 7 Dec 2024 15:51:36 +0900
Masami Hiramatsu (Google) [off-list ref] wrote:

quoted

This checks the handler is called with preempt off.

On x86_64, the ftrace_graph_func calls function_graph_enter_regs() with
ftrace_test_recursion_trylock() as below;

void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
		       struct ftrace_ops *op, struct ftrace_regs *fregs)
{
	struct pt_regs *regs = &arch_ftrace_regs(fregs)->regs;
	unsigned long *stack = (unsigned long *)kernel_stack_pointer(regs);
	unsigned long return_hooker = (unsigned long)&return_to_handler;
	unsigned long *parent = (unsigned long *)stack;
	int bit;

	if (unlikely(skip_ftrace_return()))
		return;

	bit = ftrace_test_recursion_trylock(ip, *parent);
	if (bit < 0)
		return;

	if (!function_graph_enter_regs(*parent, ip, 0, parent, fregs))
		*parent = return_hooker;

	ftrace_test_recursion_unlock(bit);
}

However, arm64 version does not;

Hmm, I think we can move that recursion check out of the arch/x86 code
and into ftrace_graph_enter_regs().

OK, that's reasonable.

Thanks,

-- Steve

-- 
Masami Hiramatsu (Google) [off-list ref]