[PATCH] gpiolib: protect gpio_chip with SRCU in array_info paths in multi get/set

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

During the locking rework in GPIOLIB, we omitted one important use-case,
namely: setting and getting values for GPIO descriptor arrays with
array_info present.

This patch does two things: first it makes struct gpio_array store the
address of the underlying GPIO device and not chip. Next: it protects
the chip with SRCU from removal in gpiod_get_array_value_complex() and
gpiod_set_array_value_complex().

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
---
David Lechner's series made me realize that we don't use SRCU to protect
the GPIO chip in case where array_info is available in multiple get/set
routines. This addresses it. The changes here could potentially be split
into two separate commits but I want to easily backport it and it works
together as well.

 drivers/gpio/gpiolib.c | 48 +++++++++++++++++++++++++++++-------------
 drivers/gpio/gpiolib.h |  4 ++--
 2 files changed, 35 insertions(+), 17 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 679ed764cb14..6e630680be52 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3129,6 +3129,8 @@ static int gpiod_get_raw_value_commit(const struct gpio_desc *desc)
 static int gpio_chip_get_multiple(struct gpio_chip *gc,
 				  unsigned long *mask, unsigned long *bits)
 {
+	lockdep_assert_held(&gc->gpiodev->srcu);
+
 	if (gc->get_multiple)
 		return gc->get_multiple(gc, mask, bits);
 	if (gc->get) {
@@ -3159,6 +3161,7 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
 				  struct gpio_array *array_info,
 				  unsigned long *value_bitmap)
 {
+	struct gpio_chip *gc;
 	int ret, i = 0;
 
 	/*
@@ -3170,10 +3173,15 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
 	    array_size <= array_info->size &&
 	    (void *)array_info == desc_array + array_info->size) {
 		if (!can_sleep)
-			WARN_ON(array_info->chip->can_sleep);
+			WARN_ON(array_info->gdev->can_sleep);
 
-		ret = gpio_chip_get_multiple(array_info->chip,
-					     array_info->get_mask,
+		guard(srcu)(&array_info->gdev->srcu);
+		gc = srcu_dereference(array_info->gdev->chip,
+				      &array_info->gdev->srcu);
+		if (!gc)
+			return -ENODEV;
+
+		ret = gpio_chip_get_multiple(gc, array_info->get_mask,
 					     value_bitmap);
 		if (ret)
 			return ret;
@@ -3454,6 +3462,8 @@ static void gpiod_set_raw_value_commit(struct gpio_desc *desc, bool value)
 static void gpio_chip_set_multiple(struct gpio_chip *gc,
 				   unsigned long *mask, unsigned long *bits)
 {
+	lockdep_assert_held(&gc->gpiodev->srcu);
+
 	if (gc->set_multiple) {
 		gc->set_multiple(gc, mask, bits);
 	} else {
@@ -3471,6 +3481,7 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
 				  struct gpio_array *array_info,
 				  unsigned long *value_bitmap)
 {
+	struct gpio_chip *gc;
 	int i = 0;
 
 	/*
@@ -3482,14 +3493,19 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
 	    array_size <= array_info->size &&
 	    (void *)array_info == desc_array + array_info->size) {
 		if (!can_sleep)
-			WARN_ON(array_info->chip->can_sleep);
+			WARN_ON(array_info->gdev->can_sleep);
+
+		guard(srcu)(&array_info->gdev->srcu);
+		gc = srcu_dereference(array_info->gdev->chip,
+				      &array_info->gdev->srcu);
+		if (!gc)
+			return -ENODEV;
 
 		if (!raw && !bitmap_empty(array_info->invert_mask, array_size))
 			bitmap_xor(value_bitmap, value_bitmap,
 				   array_info->invert_mask, array_size);
 
-		gpio_chip_set_multiple(array_info->chip, array_info->set_mask,
-				       value_bitmap);
+		gpio_chip_set_multiple(gc, array_info->set_mask, value_bitmap);
 
 		i = find_first_zero_bit(array_info->set_mask, array_size);
 		if (i == array_size)
@@ -4751,8 +4767,8 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
 {
 	struct gpio_desc *desc;
 	struct gpio_descs *descs;
+	struct gpio_device *gdev;
 	struct gpio_array *array_info = NULL;
-	struct gpio_chip *gc;
 	int count, bitmap_size;
 	size_t descs_size;
 
@@ -4774,7 +4790,7 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
 
 		descs->desc[descs->ndescs] = desc;
 
-		gc = gpiod_to_chip(desc);
+		gdev = gpiod_to_gpio_device(desc);
 		/*
 		 * If pin hardware number of array member 0 is also 0, select
 		 * its chip as a candidate for fast bitmap processing path.
@@ -4782,8 +4798,8 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
 		if (descs->ndescs == 0 && gpio_chip_hwgpio(desc) == 0) {
 			struct gpio_descs *array;
 
-			bitmap_size = BITS_TO_LONGS(gc->ngpio > count ?
-						    gc->ngpio : count);
+			bitmap_size = BITS_TO_LONGS(gdev->ngpio > count ?
+						    gdev->ngpio : count);
 
 			array = krealloc(descs, descs_size +
 					 struct_size(array_info, invert_mask, 3 * bitmap_size),
@@ -4803,7 +4819,7 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
 
 			array_info->desc = descs->desc;
 			array_info->size = count;
-			array_info->chip = gc;
+			array_info->gdev = gdev;
 			bitmap_set(array_info->get_mask, descs->ndescs,
 				   count - descs->ndescs);
 			bitmap_set(array_info->set_mask, descs->ndescs,
@@ -4816,7 +4832,7 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
 			continue;
 
 		/* Unmark array members which don't belong to the 'fast' chip */
-		if (array_info->chip != gc) {
+		if (array_info->gdev != gdev) {
 			__clear_bit(descs->ndescs, array_info->get_mask);
 			__clear_bit(descs->ndescs, array_info->set_mask);
 		}
@@ -4840,8 +4856,10 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
 			}
 		} else {
 			/* Exclude open drain or open source from fast output */
-			if (gpiochip_line_is_open_drain(gc, descs->ndescs) ||
-			    gpiochip_line_is_open_source(gc, descs->ndescs))
+			if (gpiochip_line_is_open_drain(gdev->chip,
+							descs->ndescs) ||
+			    gpiochip_line_is_open_source(gdev->chip,
+							 descs->ndescs))
 				__clear_bit(descs->ndescs,
 					    array_info->set_mask);
 			/* Identify 'fast' pins which require invertion */
@@ -4853,7 +4871,7 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
 	if (array_info)
 		dev_dbg(dev,
 			"GPIO array info: chip=%s, size=%d, get_mask=%lx, set_mask=%lx, invert_mask=%lx\n",
-			array_info->chip->label, array_info->size,
+			array_info->gdev->label, array_info->size,
 			*array_info->get_mask, *array_info->set_mask,
 			*array_info->invert_mask);
 	return descs;
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 83690f72f7e5..147156ec502b 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -114,7 +114,7 @@ extern const char *const gpio_suffixes[];
  *
  * @desc:		Array of pointers to the GPIO descriptors
  * @size:		Number of elements in desc
- * @chip:		Parent GPIO chip
+ * @gdev:		Parent GPIO device
  * @get_mask:		Get mask used in fastpath
  * @set_mask:		Set mask used in fastpath
  * @invert_mask:	Invert mask used in fastpath
@@ -126,7 +126,7 @@ extern const char *const gpio_suffixes[];
 struct gpio_array {
 	struct gpio_desc	**desc;
 	unsigned int		size;
-	struct gpio_chip	*chip;
+	struct gpio_device	*gdev;
 	unsigned long		*get_mask;
 	unsigned long		*set_mask;
 	unsigned long		invert_mask[];
-- 
2.45.2