[PATCH v2 7/7] gpiolib: use bitmap_zalloc() for fastpath bitmaps

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Currently, struct gpio_array embeds invert_mask[] as a flexible array
member, and gpio_descs_alloc() allocates the descriptor array,
struct gpio_array, and all three fastpath bitmaps in a single kzalloc()
call using manual BITS_TO_LONGS() calculations and pointer arithmetic.
This exposes gpiolib to the underlying unsigned long representation
used by bitmaps rather than respecting the bitmap abstraction.

Convert invert_mask in struct gpio_array to a pointer and allocate each
of the three fastpath bitmaps individually via bitmap_zalloc(), freeing
them via bitmap_free() on fastpath cancellation and array disposal.

Although this adds three slab allocations when the fastpath is active,
packing all three masks into a single bitmap_zalloc() call would still
require rounding the bit count up to BITS_PER_LONG and slicing the
buffer with unsigned long pointer arithmetic, adding a second
allocation and extra free paths without achieving bitmap API
abstraction.

Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/gpio/gpiolib.c | 47 +++++++++++++++++++++++++++++++++++++----------
 drivers/gpio/gpiolib.h |  2 +-
 2 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index cf311c1a707c..bba4e5bb125f 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -5208,13 +5208,28 @@ static void gpiochip_free_hogs(struct gpio_chip *gc)
 		gpiochip_free_own_desc(desc);
 }
 
-static struct gpio_descs *gpio_descs_alloc(unsigned int count, struct gpio_desc *first_desc)
+static void gpio_descs_free_fastpath(struct gpio_descs *descs)
+{
+	struct gpio_array *array_info;
+
+	array_info = descs->info;
+	if (!array_info)
+		return;
+
+	bitmap_free(array_info->get_mask);
+	bitmap_free(array_info->set_mask);
+	bitmap_free(array_info->invert_mask);
+	descs->info = NULL;
+}
+
+static struct gpio_descs *gpio_descs_alloc(unsigned int count,
+					   struct gpio_desc *first_desc)
 {
 	struct gpio_device *gdev = gpiod_to_gpio_device(first_desc);
+	struct gpio_descs *descs __free(gpiod_put_array) = NULL;
 	struct gpio_array *array_info;
-	struct gpio_descs *descs;
 	size_t descs_size, alloc_size;
-	unsigned int bitmap_size;
+	unsigned int nbits;
 
 	/*
 	 * If pin hardware number of array member 0 is also 0, select
@@ -5224,25 +5239,36 @@ static struct gpio_descs *gpio_descs_alloc(unsigned int count, struct gpio_desc
 		return kzalloc_flex(*descs, desc, count);
 
 	descs_size = struct_size(descs, desc, count);
-	bitmap_size = BITS_TO_LONGS(max(gdev->ngpio, count));
-	alloc_size = descs_size + struct_size(array_info, invert_mask, 3 * bitmap_size);
+	alloc_size = descs_size + sizeof(*array_info);
 
 	descs = kzalloc(alloc_size, GFP_KERNEL);
 	if (!descs)
 		return NULL;
 
 	array_info = (void *)descs + descs_size;
-	array_info->get_mask = array_info->invert_mask + bitmap_size;
-	array_info->set_mask = array_info->get_mask + bitmap_size;
+	descs->info = array_info;
+
+	nbits = max(gdev->ngpio, count);
+
+	array_info->get_mask = bitmap_zalloc(nbits, GFP_KERNEL);
+	if (!array_info->get_mask)
+		return NULL;
+
+	array_info->set_mask = bitmap_zalloc(nbits, GFP_KERNEL);
+	if (!array_info->set_mask)
+		return NULL;
+
+	array_info->invert_mask = bitmap_zalloc(nbits, GFP_KERNEL);
+	if (!array_info->invert_mask)
+		return NULL;
 
 	array_info->desc = descs->desc;
 	array_info->size = count;
 	array_info->gdev = gdev;
 	bitmap_set(array_info->get_mask, 0, count);
 	bitmap_set(array_info->set_mask, 0, count);
-	descs->info = array_info;
 
-	return descs;
+	return_ptr(descs);
 }
 
 static void gpio_descs_check_fastpath(struct gpio_descs *descs,
@@ -5274,7 +5300,7 @@ static void gpio_descs_check_fastpath(struct gpio_descs *descs,
 		 * hardware number is different from its array index.
 		 */
 		if (bitmap_full(array_info->get_mask, idx)) {
-			descs->info = NULL;
+			gpio_descs_free_fastpath(descs);
 		} else {
 			__clear_bit(idx, array_info->get_mask);
 			__clear_bit(idx, array_info->set_mask);
@@ -5397,6 +5423,7 @@ void gpiod_put_array(struct gpio_descs *descs)
 	for (i = 0; i < descs->ndescs; i++)
 		gpiod_put(descs->desc[i]);
 
+	gpio_descs_free_fastpath(descs);
 	kfree(descs);
 }
 EXPORT_SYMBOL_GPL(gpiod_put_array);
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 650a702741df..de1795c9be3d 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -135,7 +135,7 @@ struct gpio_array {
 	struct gpio_device	*gdev;
 	unsigned long		*get_mask;
 	unsigned long		*set_mask;
-	unsigned long		invert_mask[];
+	unsigned long		*invert_mask;
 };
 
 #define for_each_gpio_desc(gc, desc)					\

-- 
2.56.0.385.gac671c819a-goog