On 2021/04/29 16:02, Rocco Yue wrote:

+static void rtnl_print_btrace(struct timer_list *unused)
+{
+	pr_info("----------- %s start -----------\n", __func__);
+	pr_info("%s[%d][%c] hold rtnl_lock more than 2 sec, start time: %llu\n",
+		rtnl_instance.task->comm,
+		rtnl_instance.pid,
+		task_state_to_char(rtnl_instance.task),
+		rtnl_instance.start_time);
+	stack_trace_print(rtnl_instance.addrs, rtnl_instance.nr_entries, 0);

Do we want to print same traces every 2 seconds? 

Since it is possible to stall for e.g. 30 seconds, printing either only upon
first call to rtnl_print_btrace() for each stalling duration or only upon
end of stalling duration (i.e. from rtnl_relase_btrace()) is better?

+	show_stack(rtnl_instance.task, NULL, KERN_DEBUG);

Why KERN_DEBUG ?

If you retrieve the output via dmesg, KERN_DEBUG would be fine.
But for syzkaller (which counts on printk() messages being printed to
consoles), KERN_INFO (or default) is expected.

+	pr_info("------------ %s end -----------\n", __func__);
+}
+
+static void rtnl_relase_btrace(void)
+{
+	rtnl_instance.end_time = sched_clock();
+

You should del_timer_sync() here than

+	if (rtnl_instance.end_time - rtnl_instance.start_time > 2000000000ULL) {
+		pr_info("rtnl_lock is held by [%d] from [%llu] to [%llu]\n",
+			rtnl_instance.pid,
+			rtnl_instance.start_time,
+			rtnl_instance.end_time);
+	}
+
+	del_timer(&rtnl_chk_timer);

here in order to make sure that end message is printed only after
rtnl_print_btrace() messages are printed.

+}
+#endif
+

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