Input: sysrq - pass along lone Alt + SysRq

When user presses and releases Alt + SysRq without pressing any of the
hot keys re-inject the combination and pass it on to userspace instead
of suppressing it - maybe he or she wanted to take print screen
instead of invoking SysRq handler.

Also pass along release events for keys that have been pressed before
SysRq mode has been invoked so that keys do not appear to be "stuck".

Acked-by: Jason Wessel <[e-mail]>
Tested-by: Jason Wessel <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/char/sysrq.c

···
 #ifdef CONFIG_INPUT
 
 /* Simple translation table for the SysRq keys */
-static const unsigned char sysrq_xlate[KEY_MAX + 1] =
+static const unsigned char sysrq_xlate[KEY_CNT] =
         "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
         "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
         "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
···
         "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
         "\r\000/";                                      /* 0x60 - 0x6f */
 
-static bool sysrq_down;
-static int sysrq_alt_use;
-static int sysrq_alt;
-static DEFINE_SPINLOCK(sysrq_event_lock);
+struct sysrq_state {
+	struct input_handle handle;
+	struct work_struct reinject_work;
+	unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
+	unsigned int alt;
+	unsigned int alt_use;
+	bool active;
+	bool need_reinject;
+};
 
-static bool sysrq_filter(struct input_handle *handle, unsigned int type,
-		         unsigned int code, int value)
+static void sysrq_reinject_alt_sysrq(struct work_struct *work)
 {
+	struct sysrq_state *sysrq =
+			container_of(work, struct sysrq_state, reinject_work);
+	struct input_handle *handle = &sysrq->handle;
+	unsigned int alt_code = sysrq->alt_use;
+
+	if (sysrq->need_reinject) {
+		/* Simulate press and release of Alt + SysRq */
+		input_inject_event(handle, EV_KEY, alt_code, 1);
+		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
+		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
+
+		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
+		input_inject_event(handle, EV_KEY, alt_code, 0);
+		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
+	}
+}
+
+static bool sysrq_filter(struct input_handle *handle,
+			 unsigned int type, unsigned int code, int value)
+{
+	struct sysrq_state *sysrq = handle->private;
+	bool was_active = sysrq->active;
 	bool suppress;
 
-	/* We are called with interrupts disabled, just take the lock */
-	spin_lock(&sysrq_event_lock);
+	switch (type) {
 
-	if (type != EV_KEY)
-		goto out;
-
-	switch (code) {
-
-	case KEY_LEFTALT:
-	case KEY_RIGHTALT:
-		if (value)
-			sysrq_alt = code;
-		else {
-			if (sysrq_down && code == sysrq_alt_use)
-				sysrq_down = false;
-
-			sysrq_alt = 0;
-		}
+	case EV_SYN:
+		suppress = false;
 		break;
 
-	case KEY_SYSRQ:
-		if (value == 1 && sysrq_alt) {
-			sysrq_down = true;
-			sysrq_alt_use = sysrq_alt;
+	case EV_KEY:
+		switch (code) {
+
+		case KEY_LEFTALT:
+		case KEY_RIGHTALT:
+			if (!value) {
+				/* One of ALTs is being released */
+				if (sysrq->active && code == sysrq->alt_use)
+					sysrq->active = false;
+
+				sysrq->alt = KEY_RESERVED;
+
+			} else if (value != 2) {
+				sysrq->alt = code;
+				sysrq->need_reinject = false;
+			}
+			break;
+
+		case KEY_SYSRQ:
+			if (value == 1 && sysrq->alt != KEY_RESERVED) {
+				sysrq->active = true;
+				sysrq->alt_use = sysrq->alt;
+				/*
+				 * If nothing else will be pressed we'll need
+				 * to * re-inject Alt-SysRq keysroke.
+				 */
+				sysrq->need_reinject = true;
+			}
+
+			/*
+			 * Pretend that sysrq was never pressed at all. This
+			 * is needed to properly handle KGDB which will try
+			 * to release all keys after exiting debugger. If we
+			 * do not clear key bit it KGDB will end up sending
+			 * release events for Alt and SysRq, potentially
+			 * triggering print screen function.
+			 */
+			if (sysrq->active)
+				clear_bit(KEY_SYSRQ, handle->dev->key);
+
+			break;
+
+		default:
+			if (sysrq->active && value && value != 2) {
+				sysrq->need_reinject = false;
+				__handle_sysrq(sysrq_xlate[code], true);
+			}
+			break;
+		}
+
+		suppress = sysrq->active;
+
+		if (!sysrq->active) {
+			/*
+			 * If we are not suppressing key presses keep track of
+			 * keyboard state so we can release keys that have been
+			 * pressed before entering SysRq mode.
+			 */
+			if (value)
+				set_bit(code, sysrq->key_down);
+			else
+				clear_bit(code, sysrq->key_down);
+
+			if (was_active)
+				schedule_work(&sysrq->reinject_work);
+
+		} else if (value == 0 &&
+			   test_and_clear_bit(code, sysrq->key_down)) {
+			/*
+			 * Pass on release events for keys that was pressed before
+			 * entering SysRq mode.
+			 */
+			suppress = false;
 		}
 		break;
 
 	default:
-		if (sysrq_down && value && value != 2)
-			__handle_sysrq(sysrq_xlate[code], true);
+		suppress = sysrq->active;
 		break;
 	}
-
-out:
-	suppress = sysrq_down;
-	spin_unlock(&sysrq_event_lock);
 
 	return suppress;
 }
···
 			 struct input_dev *dev,
 			 const struct input_device_id *id)
 {
-	struct input_handle *handle;
+	struct sysrq_state *sysrq;
 	int error;
 
-	sysrq_down = false;
-	sysrq_alt = 0;
-
-	handle = kzalloc(sizeof(struct input_handle), GFP_KERNEL);
-	if (!handle)
+	sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
+	if (!sysrq)
 		return -ENOMEM;
 
-	handle->dev = dev;
-	handle->handler = handler;
-	handle->name = "sysrq";
+	INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);
 
-	error = input_register_handle(handle);
+	sysrq->handle.dev = dev;
+	sysrq->handle.handler = handler;
+	sysrq->handle.name = "sysrq";
+	sysrq->handle.private = sysrq;
+
+	error = input_register_handle(&sysrq->handle);
 	if (error) {
 		pr_err("Failed to register input sysrq handler, error %d\n",
 			error);
 		goto err_free;
 	}
 
-	error = input_open_device(handle);
+	error = input_open_device(&sysrq->handle);
 	if (error) {
 		pr_err("Failed to open input device, error %d\n", error);
 		goto err_unregister;
···
 	return 0;
 
  err_unregister:
-	input_unregister_handle(handle);
+	input_unregister_handle(&sysrq->handle);
  err_free:
-	kfree(handle);
+	kfree(sysrq);
 	return error;
 }
 
 static void sysrq_disconnect(struct input_handle *handle)
 {
+	struct sysrq_state *sysrq = handle->private;
+
 	input_close_device(handle);
+	cancel_work_sync(&sysrq->reinject_work);
 	input_unregister_handle(handle);
-	kfree(handle);
+	kfree(sysrq);
 }
 
 /*