Merge tag 'kgdb-6.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux

Pull kgdb updates from Daniel Thompson:
 "Nine patches this cycle and they split into just three topics:

   - Adopt coccinelle's recommendation to adopt str_plural()

   - A set of seven patches to refactor kdb_read() to improve both code
     clarity and its discipline with respect to fixed size buffers.

     This isn't just a refactor. Between them these also fix a cursor
     movement redraw problem and two buffer overflows (one latent and
     one real, albeit difficult to tickle).

   - Fix an NMI-safety problem when enqueuing kdb's keyboard reset code

  I wrote eight of the nine patches in this collection so many thanks to
  Doug Anderson for the reviews. The changes that affects
  drivers/tty/serial is acked by Greg KH"

* tag 'kgdb-6.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux:
  serial: kgdboc: Fix NMI-safety problems from keyboard reset code
  kdb: Simplify management of tmpbuffer in kdb_read()
  kdb: Replace double memcpy() with memmove() in kdb_read()
  kdb: Use format-specifiers rather than memset() for padding in kdb_read()
  kdb: Merge identical case statements in kdb_read()
  kdb: Fix console handling when editing and tab-completing commands
  kdb: Use format-strings rather than '\0' injection in kdb_read()
  kdb: Fix buffer overflow during tab-complete
  kdb: Use str_plural() to fix Coccinelle warning

1 files changed, 29 insertions, 1 deletions

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 7ce7bb164005..58ea1e1391ce 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -19,6 +19,7 @@
 #include <linux/console.h>
 #include <linux/vt_kern.h>
 #include <linux/input.h>
+#include <linux/irq_work.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/serial_core.h>
@@ -48,6 +49,25 @@ static struct kgdb_io		kgdboc_earlycon_io_ops;
 static int                      (*earlycon_orig_exit)(struct console *con);
 #endif /* IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */
 
+/*
+ * When we leave the debug trap handler we need to reset the keyboard status
+ * (since the original keyboard state gets partially clobbered by kdb use of
+ * the keyboard).
+ *
+ * The path to deliver the reset is somewhat circuitous.
+ *
+ * To deliver the reset we register an input handler, reset the keyboard and
+ * then deregister the input handler. However, to get this done right, we do
+ * have to carefully manage the calling context because we can only register
+ * input handlers from task context.
+ *
+ * In particular we need to trigger the action from the debug trap handler with
+ * all its NMI and/or NMI-like oddities. To solve this the kgdboc trap exit code
+ * (the "post_exception" callback) uses irq_work_queue(), which is NMI-safe, to
+ * schedule a callback from a hardirq context. From there we have to defer the
+ * work again, this time using schedule_work(), to get a callback using the
+ * system workqueue, which runs in task context.
+ */
 #ifdef CONFIG_KDB_KEYBOARD
 static int kgdboc_reset_connect(struct input_handler *handler,
 				struct input_dev *dev,
@@ -99,10 +119,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
 
 static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
 
+static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
+{
+	schedule_work(&kgdboc_restore_input_work);
+}
+
+static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
+
 static void kgdboc_restore_input(void)
 {
 	if (likely(system_state == SYSTEM_RUNNING))
-		schedule_work(&kgdboc_restore_input_work);
+		irq_work_queue(&kgdboc_restore_input_irq_work);
 }
 
 static int kgdboc_register_kbd(char **cptr)
@@ -133,6 +160,7 @@ static void kgdboc_unregister_kbd(void)
 			i--;
 		}
 	}
+	irq_work_sync(&kgdboc_restore_input_irq_work);
 	flush_work(&kgdboc_restore_input_work);
 }
 #else /* ! CONFIG_KDB_KEYBOARD */