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...

Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

2 files changed, 24 insertions, 0 deletions

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 0d7c08784efb..3c1ad4e03543 100644
--- 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(void)
          */
         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();
diff --git a/kernel/debug/gdbstub.c b/kernel/debug/gdbstub.c
index 5a155742ae96..ce615e064482 100644
--- a/kernel/debug/gdbstub.c
+++ b/kernel/debug/gdbstub.c
@@ -1111,6 +1111,13 @@ void gdbstub_exit(int status)
         unsigned char checksum, ch, buffer[3];
         int loop;
 
+        if (!kgdb_connected)
+                return;
+        kgdb_connected = 0;
+
+        if (!dbg_io_ops || dbg_kdb_mode)
+                return;
+
         buffer[0] = 'W';
         buffer[1] = hex_asc_hi(status);
         buffer[2] = hex_asc_lo(status);