From: Jason Wessel <jason.wessel@windriver.com>
Subject: [PATCH] kgdb,debug-core,gdbstub: Hook the reboot notifier for debugger detach

The gdbstub and kdb should get detached if the system is rebooting.
Calling gdbstub_exit() will set the proper debug core state and send a
message to any debugger that is connected to correctly detach.

An attached debugger will receive the exit code from
include/linux/reboot.h based on SYS_HALT, SYS_REBOOT, etc...

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
 kernel/debug/debug_core.c |   17 +++++++++++++++++
 kernel/debug/gdbstub.c    |    5 ++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -41,6 +41,7 @@
 #include <linux/delay.h>
 #include <linux/sched.h>
 #include <linux/sysrq.h>
+#include <linux/reboot.h>
 #include <linux/init.h>
 #include <linux/kgdb.h>
 #include <linux/kdb.h>
@@ -784,6 +785,20 @@ void __init dbg_late_init(void)
 	kdb_init(KDB_INIT_FULL);
 }
 
+static int
+dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
+{
+	if (!dbg_kdb_mode)
+		gdbstub_exit(code);
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block dbg_reboot_notifier = {
+	.notifier_call		= dbg_notify_reboot,
+	.next			= NULL,
+	.priority		= INT_MAX,
+};
+
 static void kgdb_register_callbacks(void)
 {
 	if (!kgdb_io_module_registered) {
@@ -791,6 +806,7 @@ static void kgdb_register_callbacks(void
 		kgdb_arch_init();
 		if (!dbg_is_early)
 			kgdb_arch_late();
+		register_reboot_notifier(&dbg_reboot_notifier);
 		atomic_notifier_chain_register(&panic_notifier_list,
 					       &kgdb_panic_event_nb);
 #ifdef CONFIG_MAGIC_SYSRQ
@@ -812,6 +828,7 @@ static void kgdb_unregister_callbacks(vo
 	 */
 	if (kgdb_io_module_registered) {
 		kgdb_io_module_registered = 0;
+		unregister_reboot_notifier(&dbg_reboot_notifier);
 		atomic_notifier_chain_unregister(&panic_notifier_list,
 					       &kgdb_panic_event_nb);
 		kgdb_arch_exit();
--- a/kernel/debug/gdbstub.c
+++ b/kernel/debug/gdbstub.c
@@ -1110,8 +1110,11 @@ void gdbstub_exit(int status)
 {
 	unsigned char checksum, ch, buffer[3];
 	int loop;
+	if (!kgdb_connected)
+		return;
+	kgdb_connected = 0;
 
-	if (!dbg_io_ops || !kgdb_connected)
+	if (!dbg_io_ops || dbg_kdb_mode)
 		return;
 
 	buffer[0] = 'W';