From: John Ogness <john.ogness@linutronix.de>
Date: Tue, 26 Sep 2023 13:04:15 +0000
Subject: [PATCH 125/134] printk: nbcon: Stop threads on shutdown/reboot
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz

Register a syscore_ops shutdown function to stop all threaded
printers on shutdown/reboot. This allows printk to transition back
to atomic printing in order to provide a robust mechanism for
outputting the final messages.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/printk/nbcon.c |   31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -8,6 +8,7 @@
 #include <linux/kthread.h>
 #include <linux/slab.h>
 #include <linux/serial_core.h>
+#include <linux/syscore_ops.h>
 #include "printk_ringbuffer.h"
 #include "internal.h"
 /*
@@ -1577,3 +1578,33 @@ void nbcon_release(struct uart_port *up)
 	con->locked_port = false;
 }
 EXPORT_SYMBOL_GPL(nbcon_release);
+
+/**
+ * printk_kthread_shutdown - shutdown all threaded printers
+ *
+ * On system shutdown all threaded printers are stopped. This allows printk
+ * to transition back to atomic printing, thus providing a robust mechanism
+ * for the final shutdown/reboot messages to be output.
+ */
+static void printk_kthread_shutdown(void)
+{
+	struct console *con;
+
+	console_list_lock();
+	for_each_console(con) {
+		if (con->flags & CON_NBCON)
+			nbcon_kthread_stop(con);
+	}
+	console_list_unlock();
+}
+
+static struct syscore_ops printk_syscore_ops = {
+	.shutdown = printk_kthread_shutdown,
+};
+
+static int __init printk_init_ops(void)
+{
+	register_syscore_ops(&printk_syscore_ops);
+	return 0;
+}
+device_initcall(printk_init_ops);