hung_task: print message when hung_task_warnings gets down to zero.

It's useful to report it when hung_task_warnings gets down to zero, so
that we can know if kernel log was lost or there is no hung task was
detected.

Link: https://lkml.kernel.org/r/20230201135416.GA6560@didi-ThinkCentre-M920t-N000
Signed-off-by: fuyuanli <fuyuanli@didiglobal.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kernel/hung_task.c

@@ -142,6 +142,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 
 		if (sysctl_hung_task_all_cpu_backtrace)
 			hung_task_show_all_bt = true;
+		if (!sysctl_hung_task_warnings)
+			pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
 	}
 
 	touch_nmi_watchdog();