Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion

On 2021/10/12 下午8:17, Steven Rostedt wrote:

On Tue, 12 Oct 2021 13:40:08 +0800
王贇 [off-list ref] wrote:

quoted

@@ -52,11 +52,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 	bit = ftrace_test_recursion_trylock(ip, parent_ip);
 	if (WARN_ON_ONCE(bit < 0))
 		return;
-	/*
-	 * A variant of synchronize_rcu() is used to allow patching functions
-	 * where RCU is not watching, see klp_synchronize_transition().
-	 */

I have to take a deeper look at this patch set, but do not remove this
comment, as it explains the protection here, that is not obvious with the
changes you made.

Will keep that in v2.

Regards,
Michael Wang

-- Steve

quoted

-	preempt_disable_notrace();

 	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
 				      stack_node);