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Commit 512b9385 authored by Daniel Thompson's avatar Daniel Thompson Committed by Greg Kroah-Hartman
Browse files

serial: kgdboc: Fix NMI-safety problems from keyboard reset code 



commit b2aba15ad6f908d1a620fd97f6af5620c3639742 upstream.

Currently, when kdb is compiled with keyboard support, then we will use
schedule_work() to provoke reset of the keyboard status.  Unfortunately
schedule_work() gets called from the kgdboc post-debug-exception
handler.  That risks deadlock since schedule_work() is not NMI-safe and,
even on platforms where the NMI is not directly used for debugging, the
debug trap can have NMI-like behaviour depending on where breakpoints
are placed.

Fix this by using the irq work system, which is NMI-safe, to defer the
call to schedule_work() to a point when it is safe to call.

Reported-by: default avatarLiuye <liu.yeC@h3c.com>
Closes: https://lore.kernel.org/all/20240228025602.3087748-1-liu.yeC@h3c.com/


Cc: stable@vger.kernel.org
Reviewed-by: default avatarDouglas Anderson <dianders@chromium.org>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240424-kgdboc_fix_schedule_work-v2-1-50f5a490aec5@linaro.org


Signed-off-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 3fe17266

drivers/tty/serial/kgdboc.c

+29 −1
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include <linux/console.h>

#include <linux/vt_kern.h>

#include <linux/input.h>

#include <linux/irq_work.h>

#include <linux/module.h>



#define MAX_CONFIG_LEN		40
@@ -35,6 +36,25 @@ static int kgdboc_use_kms; /* 1 if we use kernel mode switching */ 
static struct tty_driver	*kgdb_tty_driver;

static int			kgdb_tty_line;



/*

 * 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,
@@ -86,10 +106,17 @@ 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)
@@ -120,6 +147,7 @@ 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 */