gpio: protect the pointer to gpio_chip in gpio_device with SRCU

Ensure we cannot crash if the GPIO device gets unregistered (and the
chip pointer set to NULL) during any of the API calls.

To that end: wait for all users of gdev->chip to exit their read-only
SRCU critical sections in gpiochip_remove().

For brevity: add a guard class which can be instantiated at the top of
every function requiring read-only access to the chip pointer and use it
in all API calls taking a GPIO descriptor as argument. In places where
we only deal with the GPIO device - use regular guard() helpers and
rcu_dereference() for chip access. Do the same in API calls taking a
const pointer to gpio_desc.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

1 files changed, 173 insertions, 84 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 4e0c6df4a880..1a9d045b5a6b 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -216,7 +216,7 @@ struct gpio_chip *gpiod_to_chip(const struct gpio_desc *desc)
 {
 	if (!desc)
 		return NULL;
-	return desc->gdev->chip;
+	return rcu_dereference(desc->gdev->chip);
 }
 EXPORT_SYMBOL_GPL(gpiod_to_chip);
 
@@ -285,7 +285,7 @@ EXPORT_SYMBOL(gpio_device_get_label);
  */
 struct gpio_chip *gpio_device_get_chip(struct gpio_device *gdev)
 {
-	return gdev->chip;
+	return rcu_dereference(gdev->chip);
 }
 EXPORT_SYMBOL_GPL(gpio_device_get_chip);
 
@@ -325,12 +325,21 @@ static int gpiochip_find_base_unlocked(int ngpio)
  */
 int gpiod_get_direction(struct gpio_desc *desc)
 {
-	struct gpio_chip *gc;
 	unsigned long flags;
 	unsigned int offset;
 	int ret;
 
-	gc = gpiod_to_chip(desc);
+	/*
+	 * We cannot use VALIDATE_DESC() as we must not return 0 for a NULL
+	 * descriptor like we usually do.
+	 */
+	if (!desc || IS_ERR(desc))
+		return -EINVAL;
+
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return -ENODEV;
+
 	offset = gpio_chip_hwgpio(desc);
 	flags = READ_ONCE(desc->flags);
 
@@ -342,10 +351,10 @@ int gpiod_get_direction(struct gpio_desc *desc)
 	    test_bit(FLAG_IS_OUT, &flags))
 		return 0;
 
-	if (!gc->get_direction)
+	if (!guard.gc->get_direction)
 		return -ENOTSUPP;
 
-	ret = gc->get_direction(gc, offset);
+	ret = guard.gc->get_direction(guard.gc, offset);
 	if (ret < 0)
 		return ret;
 
@@ -421,6 +430,7 @@ static struct gpio_desc *gpio_name_to_desc(const char * const name)
 {
 	struct gpio_device *gdev;
 	struct gpio_desc *desc;
+	struct gpio_chip *gc;
 
 	if (!name)
 		return NULL;
@@ -429,7 +439,13 @@ static struct gpio_desc *gpio_name_to_desc(const char * const name)
 
 	list_for_each_entry_srcu(gdev, &gpio_devices, list,
 				 srcu_read_lock_held(&gpio_devices_srcu)) {
-		for_each_gpio_desc(gdev->chip, desc) {
+		guard(srcu)(&gdev->srcu);
+
+		gc = rcu_dereference(gdev->chip);
+		if (!gc)
+			continue;
+
+		for_each_gpio_desc(gc, desc) {
 			if (desc->name && !strcmp(desc->name, name))
 				return desc;
 		}
@@ -853,7 +869,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	gdev->dev.type = &gpio_dev_type;
 	gdev->dev.bus = &gpio_bus_type;
 	gdev->dev.parent = gc->parent;
-	gdev->chip = gc;
+	rcu_assign_pointer(gdev->chip, gc);
 
 	gc->gpiodev = gdev;
 	gpiochip_set_data(gc, data);
@@ -1097,7 +1113,8 @@ void gpiochip_remove(struct gpio_chip *gc)
 	synchronize_srcu(&gpio_devices_srcu);
 
 	/* Numb the device, cancelling all outstanding operations */
-	gdev->chip = NULL;
+	rcu_assign_pointer(gdev->chip, NULL);
+	synchronize_srcu(&gdev->srcu);
 	gpiochip_irqchip_remove(gc);
 	acpi_gpiochip_remove(gc);
 	of_gpiochip_remove(gc);
@@ -1156,6 +1173,7 @@ struct gpio_device *gpio_device_find(void *data,
 						  const void *data))
 {
 	struct gpio_device *gdev;
+	struct gpio_chip *gc;
 
 	/*
 	 * Not yet but in the future the spinlock below will become a mutex.
@@ -1166,8 +1184,13 @@ struct gpio_device *gpio_device_find(void *data,
 
 	guard(srcu)(&gpio_devices_srcu);
 
-	list_for_each_entry(gdev, &gpio_devices, list) {
-		if (gdev->chip && match(gdev->chip, data))
+	list_for_each_entry_srcu(gdev, &gpio_devices, list,
+				 srcu_read_lock_held(&gpio_devices_srcu)) {
+		guard(srcu)(&gdev->srcu);
+
+		gc = rcu_dereference(gdev->chip);
+
+		if (gc && match(gc, data))
 			return gpio_device_get(gdev);
 	}
 
@@ -2214,10 +2237,13 @@ EXPORT_SYMBOL_GPL(gpiochip_remove_pin_ranges);
  */
 static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
 {
-	struct gpio_chip *gc = desc->gdev->chip;
 	unsigned int offset;
 	int ret;
 
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return -ENODEV;
+
 	if (test_and_set_bit(FLAG_REQUESTED, &desc->flags))
 		return -EBUSY;
 
@@ -2231,17 +2257,17 @@ static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
 	 * before IRQs are enabled, for non-sleeping (SOC) GPIOs.
 	 */
 
-	if (gc->request) {
+	if (guard.gc->request) {
 		offset = gpio_chip_hwgpio(desc);
-		if (gpiochip_line_is_valid(gc, offset))
-			ret = gc->request(gc, offset);
+		if (gpiochip_line_is_valid(guard.gc, offset))
+			ret = guard.gc->request(guard.gc, offset);
 		else
 			ret = -EINVAL;
 		if (ret)
 			goto out_clear_bit;
 	}
 
-	if (gc->get_direction)
+	if (guard.gc->get_direction)
 		gpiod_get_direction(desc);
 
 	ret = desc_set_label(desc, label ? : "?");
@@ -2308,18 +2334,18 @@ int gpiod_request(struct gpio_desc *desc, const char *label)
 
 static bool gpiod_free_commit(struct gpio_desc *desc)
 {
-	struct gpio_chip *gc;
 	unsigned long flags;
 	bool ret = false;
 
 	might_sleep();
 
-	gc = desc->gdev->chip;
+	CLASS(gpio_chip_guard, guard)(desc);
+
 	flags = READ_ONCE(desc->flags);
 
-	if (gc && test_bit(FLAG_REQUESTED, &flags)) {
-		if (gc->free)
-			gc->free(gc, gpio_chip_hwgpio(desc));
+	if (guard.gc && test_bit(FLAG_REQUESTED, &flags)) {
+		if (guard.gc->free)
+			guard.gc->free(guard.gc, gpio_chip_hwgpio(desc));
 
 		clear_bit(FLAG_ACTIVE_LOW, &flags);
 		clear_bit(FLAG_REQUESTED, &flags);
@@ -2476,11 +2502,14 @@ static int gpio_set_config_with_argument(struct gpio_desc *desc,
 					 enum pin_config_param mode,
 					 u32 argument)
 {
-	struct gpio_chip *gc = desc->gdev->chip;
 	unsigned long config;
 
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return -ENODEV;
+
 	config = pinconf_to_config_packed(mode, argument);
-	return gpio_do_set_config(gc, gpio_chip_hwgpio(desc), config);
+	return gpio_do_set_config(guard.gc, gpio_chip_hwgpio(desc), config);
 }
 
 static int gpio_set_config_with_argument_optional(struct gpio_desc *desc,
@@ -2570,18 +2599,20 @@ int gpio_set_debounce_timeout(struct gpio_desc *desc, unsigned int debounce)
  */
 int gpiod_direction_input(struct gpio_desc *desc)
 {
-	struct gpio_chip *gc;
 	int ret = 0;
 
 	VALIDATE_DESC(desc);
-	gc = desc->gdev->chip;
+
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return -ENODEV;
 
 	/*
 	 * It is legal to have no .get() and .direction_input() specified if
 	 * the chip is output-only, but you can't specify .direction_input()
 	 * and not support the .get() operation, that doesn't make sense.
 	 */
-	if (!gc->get && gc->direction_input) {
+	if (!guard.gc->get && guard.gc->direction_input) {
 		gpiod_warn(desc,
 			   "%s: missing get() but have direction_input()\n",
 			   __func__);
@@ -2594,10 +2625,12 @@ int gpiod_direction_input(struct gpio_desc *desc)
 	 * direction (if .get_direction() is supported) else we silently
 	 * assume we are in input mode after this.
 	 */
-	if (gc->direction_input) {
-		ret = gc->direction_input(gc, gpio_chip_hwgpio(desc));
-	} else if (gc->get_direction &&
-		  (gc->get_direction(gc, gpio_chip_hwgpio(desc)) != 1)) {
+	if (guard.gc->direction_input) {
+		ret = guard.gc->direction_input(guard.gc,
+						gpio_chip_hwgpio(desc));
+	} else if (guard.gc->get_direction &&
+		  (guard.gc->get_direction(guard.gc,
+					   gpio_chip_hwgpio(desc)) != 1)) {
 		gpiod_warn(desc,
 			   "%s: missing direction_input() operation and line is output\n",
 			   __func__);
@@ -2616,28 +2649,31 @@ EXPORT_SYMBOL_GPL(gpiod_direction_input);
 
 static int gpiod_direction_output_raw_commit(struct gpio_desc *desc, int value)
 {
-	struct gpio_chip *gc = desc->gdev->chip;
-	int val = !!value;
-	int ret = 0;
+	int val = !!value, ret = 0;
+
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return -ENODEV;
 
 	/*
 	 * It's OK not to specify .direction_output() if the gpiochip is
 	 * output-only, but if there is then not even a .set() operation it
 	 * is pretty tricky to drive the output line.
 	 */
-	if (!gc->set && !gc->direction_output) {
+	if (!guard.gc->set && !guard.gc->direction_output) {
 		gpiod_warn(desc,
 			   "%s: missing set() and direction_output() operations\n",
 			   __func__);
 		return -EIO;
 	}
 
-	if (gc->direction_output) {
-		ret = gc->direction_output(gc, gpio_chip_hwgpio(desc), val);
+	if (guard.gc->direction_output) {
+		ret = guard.gc->direction_output(guard.gc,
+						 gpio_chip_hwgpio(desc), val);
 	} else {
 		/* Check that we are in output mode if we can */
-		if (gc->get_direction &&
-		    gc->get_direction(gc, gpio_chip_hwgpio(desc))) {
+		if (guard.gc->get_direction &&
+		    guard.gc->get_direction(guard.gc, gpio_chip_hwgpio(desc))) {
 			gpiod_warn(desc,
 				"%s: missing direction_output() operation\n",
 				__func__);
@@ -2647,7 +2683,7 @@ static int gpiod_direction_output_raw_commit(struct gpio_desc *desc, int value)
 		 * If we can't actively set the direction, we are some
 		 * output-only chip, so just drive the output as desired.
 		 */
-		gc->set(gc, gpio_chip_hwgpio(desc), val);
+		guard.gc->set(guard.gc, gpio_chip_hwgpio(desc), val);
 	}
 
 	if (!ret)
@@ -2763,17 +2799,20 @@ EXPORT_SYMBOL_GPL(gpiod_direction_output);
 int gpiod_enable_hw_timestamp_ns(struct gpio_desc *desc, unsigned long flags)
 {
 	int ret = 0;
-	struct gpio_chip *gc;
 
 	VALIDATE_DESC(desc);
 
-	gc = desc->gdev->chip;
-	if (!gc->en_hw_timestamp) {
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return -ENODEV;
+
+	if (!guard.gc->en_hw_timestamp) {
 		gpiod_warn(desc, "%s: hw ts not supported\n", __func__);
 		return -ENOTSUPP;
 	}
 
-	ret = gc->en_hw_timestamp(gc, gpio_chip_hwgpio(desc), flags);
+	ret = guard.gc->en_hw_timestamp(guard.gc,
+					gpio_chip_hwgpio(desc), flags);
 	if (ret)
 		gpiod_warn(desc, "%s: hw ts request failed\n", __func__);
 
@@ -2792,17 +2831,20 @@ EXPORT_SYMBOL_GPL(gpiod_enable_hw_timestamp_ns);
 int gpiod_disable_hw_timestamp_ns(struct gpio_desc *desc, unsigned long flags)
 {
 	int ret = 0;
-	struct gpio_chip *gc;
 
 	VALIDATE_DESC(desc);
 
-	gc = desc->gdev->chip;
-	if (!gc->dis_hw_timestamp) {
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return -ENODEV;
+
+	if (!guard.gc->dis_hw_timestamp) {
 		gpiod_warn(desc, "%s: hw ts not supported\n", __func__);
 		return -ENOTSUPP;
 	}
 
-	ret = gc->dis_hw_timestamp(gc, gpio_chip_hwgpio(desc), flags);
+	ret = guard.gc->dis_hw_timestamp(guard.gc, gpio_chip_hwgpio(desc),
+					 flags);
 	if (ret)
 		gpiod_warn(desc, "%s: hw ts release failed\n", __func__);
 
@@ -2821,12 +2863,13 @@ EXPORT_SYMBOL_GPL(gpiod_disable_hw_timestamp_ns);
  */
 int gpiod_set_config(struct gpio_desc *desc, unsigned long config)
 {
-	struct gpio_chip *gc;
-
 	VALIDATE_DESC(desc);
-	gc = desc->gdev->chip;
 
-	return gpio_do_set_config(gc, gpio_chip_hwgpio(desc), config);
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return -ENODEV;
+
+	return gpio_do_set_config(guard.gc, gpio_chip_hwgpio(desc), config);
 }
 EXPORT_SYMBOL_GPL(gpiod_set_config);
 
@@ -2924,10 +2967,19 @@ static int gpio_chip_get_value(struct gpio_chip *gc, const struct gpio_desc *des
 
 static int gpiod_get_raw_value_commit(const struct gpio_desc *desc)
 {
+	struct gpio_device *gdev;
 	struct gpio_chip *gc;
 	int value;
 
-	gc = desc->gdev->chip;
+	/* FIXME Unable to use gpio_chip_guard due to const desc. */
+	gdev = desc->gdev;
+
+	guard(srcu)(&gdev->srcu);
+
+	gc = rcu_dereference(gdev->chip);
+	if (!gc)
+		return -ENODEV;
+
 	value = gpio_chip_get_value(gc, desc);
 	value = value < 0 ? value : !!value;
 	trace_gpio_value(desc_to_gpio(desc), 1, value);
@@ -2953,6 +3005,14 @@ static int gpio_chip_get_multiple(struct gpio_chip *gc,
 	return -EIO;
 }
 
+/* The 'other' chip must be protected with its GPIO device's SRCU. */
+static bool gpio_device_chip_cmp(struct gpio_device *gdev, struct gpio_chip *gc)
+{
+	guard(srcu)(&gdev->srcu);
+
+	return gc == rcu_dereference(gdev->chip);
+}
+
 int gpiod_get_array_value_complex(bool raw, bool can_sleep,
 				  unsigned int array_size,
 				  struct gpio_desc **desc_array,
@@ -2990,33 +3050,36 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
 	}
 
 	while (i < array_size) {
-		struct gpio_chip *gc = desc_array[i]->gdev->chip;
 		DECLARE_BITMAP(fastpath_mask, FASTPATH_NGPIO);
 		DECLARE_BITMAP(fastpath_bits, FASTPATH_NGPIO);
 		unsigned long *mask, *bits;
 		int first, j;
 
-		if (likely(gc->ngpio <= FASTPATH_NGPIO)) {
+		CLASS(gpio_chip_guard, guard)(desc_array[i]);
+		if (!guard.gc)
+			return -ENODEV;
+
+		if (likely(guard.gc->ngpio <= FASTPATH_NGPIO)) {
 			mask = fastpath_mask;
 			bits = fastpath_bits;
 		} else {
 			gfp_t flags = can_sleep ? GFP_KERNEL : GFP_ATOMIC;
 
-			mask = bitmap_alloc(gc->ngpio, flags);
+			mask = bitmap_alloc(guard.gc->ngpio, flags);
 			if (!mask)
 				return -ENOMEM;
 
-			bits = bitmap_alloc(gc->ngpio, flags);
+			bits = bitmap_alloc(guard.gc->ngpio, flags);
 			if (!bits) {
 				bitmap_free(mask);
 				return -ENOMEM;
 			}
 		}
 
-		bitmap_zero(mask, gc->ngpio);
+		bitmap_zero(mask, guard.gc->ngpio);
 
 		if (!can_sleep)
-			WARN_ON(gc->can_sleep);
+			WARN_ON(guard.gc->can_sleep);
 
 		/* collect all inputs belonging to the same chip */
 		first = i;
@@ -3031,9 +3094,9 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
 				i = find_next_zero_bit(array_info->get_mask,
 						       array_size, i);
 		} while ((i < array_size) &&
-			 (desc_array[i]->gdev->chip == gc));
+			 gpio_device_chip_cmp(desc_array[i]->gdev, guard.gc));
 
-		ret = gpio_chip_get_multiple(gc, mask, bits);
+		ret = gpio_chip_get_multiple(guard.gc, mask, bits);
 		if (ret) {
 			if (mask != fastpath_mask)
 				bitmap_free(mask);
@@ -3174,14 +3237,16 @@ EXPORT_SYMBOL_GPL(gpiod_get_array_value);
  */
 static void gpio_set_open_drain_value_commit(struct gpio_desc *desc, bool value)
 {
-	int ret = 0;
-	struct gpio_chip *gc = desc->gdev->chip;
-	int offset = gpio_chip_hwgpio(desc);
+	int ret = 0, offset = gpio_chip_hwgpio(desc);
+
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return;
 
 	if (value) {
-		ret = gc->direction_input(gc, offset);
+		ret = guard.gc->direction_input(guard.gc, offset);
 	} else {
-		ret = gc->direction_output(gc, offset, 0);
+		ret = guard.gc->direction_output(guard.gc, offset, 0);
 		if (!ret)
 			set_bit(FLAG_IS_OUT, &desc->flags);
 	}
@@ -3199,16 +3264,18 @@ static void gpio_set_open_drain_value_commit(struct gpio_desc *desc, bool value)
  */
 static void gpio_set_open_source_value_commit(struct gpio_desc *desc, bool value)
 {
-	int ret = 0;
-	struct gpio_chip *gc = desc->gdev->chip;
-	int offset = gpio_chip_hwgpio(desc);
+	int ret = 0, offset = gpio_chip_hwgpio(desc);
+
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return;
 
 	if (value) {
-		ret = gc->direction_output(gc, offset, 1);
+		ret = guard.gc->direction_output(guard.gc, offset, 1);
 		if (!ret)
 			set_bit(FLAG_IS_OUT, &desc->flags);
 	} else {
-		ret = gc->direction_input(gc, offset);
+		ret = guard.gc->direction_input(guard.gc, offset);
 	}
 	trace_gpio_direction(desc_to_gpio(desc), !value, ret);
 	if (ret < 0)
@@ -3219,11 +3286,12 @@ static void gpio_set_open_source_value_commit(struct gpio_desc *desc, bool value
 
 static void gpiod_set_raw_value_commit(struct gpio_desc *desc, bool value)
 {
-	struct gpio_chip *gc;
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return;
 
-	gc = desc->gdev->chip;
 	trace_gpio_value(desc_to_gpio(desc), 0, value);
-	gc->set(gc, gpio_chip_hwgpio(desc), value);
+	guard.gc->set(guard.gc, gpio_chip_hwgpio(desc), value);
 }
 
 /*
@@ -3284,33 +3352,36 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
 	}
 
 	while (i < array_size) {
-		struct gpio_chip *gc = desc_array[i]->gdev->chip;
 		DECLARE_BITMAP(fastpath_mask, FASTPATH_NGPIO);
 		DECLARE_BITMAP(fastpath_bits, FASTPATH_NGPIO);
 		unsigned long *mask, *bits;
 		int count = 0;
 
-		if (likely(gc->ngpio <= FASTPATH_NGPIO)) {
+		CLASS(gpio_chip_guard, guard)(desc_array[i]);
+		if (!guard.gc)
+			return -ENODEV;
+
+		if (likely(guard.gc->ngpio <= FASTPATH_NGPIO)) {
 			mask = fastpath_mask;
 			bits = fastpath_bits;
 		} else {
 			gfp_t flags = can_sleep ? GFP_KERNEL : GFP_ATOMIC;
 
-			mask = bitmap_alloc(gc->ngpio, flags);
+			mask = bitmap_alloc(guard.gc->ngpio, flags);
 			if (!mask)
 				return -ENOMEM;
 
-			bits = bitmap_alloc(gc->ngpio, flags);
+			bits = bitmap_alloc(guard.gc->ngpio, flags);
 			if (!bits) {
 				bitmap_free(mask);
 				return -ENOMEM;
 			}
 		}
 
-		bitmap_zero(mask, gc->ngpio);
+		bitmap_zero(mask, guard.gc->ngpio);
 
 		if (!can_sleep)
-			WARN_ON(gc->can_sleep);
+			WARN_ON(guard.gc->can_sleep);
 
 		do {
 			struct gpio_desc *desc = desc_array[i];
@@ -3346,10 +3417,10 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
 				i = find_next_zero_bit(array_info->set_mask,
 						       array_size, i);
 		} while ((i < array_size) &&
-			 (desc_array[i]->gdev->chip == gc));
+			 gpio_device_chip_cmp(desc_array[i]->gdev, guard.gc));
 		/* push collected bits to outputs */
 		if (count != 0)
-			gpio_chip_set_multiple(gc, mask, bits);
+			gpio_chip_set_multiple(guard.gc, mask, bits);
 
 		if (mask != fastpath_mask)
 			bitmap_free(mask);
@@ -3505,6 +3576,7 @@ EXPORT_SYMBOL_GPL(gpiod_set_consumer_name);
  */
 int gpiod_to_irq(const struct gpio_desc *desc)
 {
+	struct gpio_device *gdev;
 	struct gpio_chip *gc;
 	int offset;
 
@@ -3516,7 +3588,13 @@ int gpiod_to_irq(const struct gpio_desc *desc)
 	if (!desc || IS_ERR(desc))
 		return -EINVAL;
 
-	gc = desc->gdev->chip;
+	gdev = desc->gdev;
+	/* FIXME Cannot use gpio_chip_guard due to const desc. */
+	guard(srcu)(&gdev->srcu);
+	gc = rcu_dereference(gdev->chip);
+	if (!gc)
+		return -ENODEV;
+
 	offset = gpio_chip_hwgpio(desc);
 	if (gc->to_irq) {
 		int retirq = gc->to_irq(gc, offset);
@@ -4696,12 +4774,20 @@ core_initcall(gpiolib_dev_init);
 
 static void gpiolib_dbg_show(struct seq_file *s, struct gpio_device *gdev)
 {
-	struct gpio_chip *gc = gdev->chip;
 	bool active_low, is_irq, is_out;
 	unsigned int gpio = gdev->base;
 	struct gpio_desc *desc;
+	struct gpio_chip *gc;
 	int value;
 
+	guard(srcu)(&gdev->srcu);
+
+	gc = rcu_dereference(gdev->chip);
+	if (!gc) {
+		seq_puts(s, "Underlying GPIO chip is gone\n");
+		return;
+	}
+
 	for_each_gpio_desc(gc, desc) {
 		guard(srcu)(&desc->srcu);
 		if (test_bit(FLAG_REQUESTED, &desc->flags)) {
@@ -4776,9 +4862,12 @@ static int gpiolib_seq_show(struct seq_file *s, void *v)
 {
 	struct gpiolib_seq_priv *priv = s->private;
 	struct gpio_device *gdev = v;
-	struct gpio_chip *gc = gdev->chip;
+	struct gpio_chip *gc;
 	struct device *parent;
 
+	guard(srcu)(&gdev->srcu);
+
+	gc = rcu_dereference(gdev->chip);
 	if (!gc) {
 		seq_printf(s, "%s%s: (dangling chip)",
 			   priv->newline ? "\n" : "",