[PATCH v3 22/24] gpio: protect the pointer to gpio_chip in gpio_device with SRCU

From: Bartosz Golaszewski
Date: Thu Feb 08 2024 - 05:06:06 EST

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

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@xxxxxxxxxx>
Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
drivers/gpio/gpiolib-cdev.c | 63 +++++----
drivers/gpio/gpiolib-sysfs.c | 57 +++++---
drivers/gpio/gpiolib.c | 257 +++++++++++++++++++++++------------
drivers/gpio/gpiolib.h | 22 ++-
4 files changed, 271 insertions(+), 128 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index e993c6a7215a..ccdeed013f6b 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -205,9 +205,9 @@ static long linehandle_ioctl(struct file *file, unsigned int cmd,
unsigned int i;
int ret;

- guard(rwsem_read)(&lh->gdev->sem);
+ guard(srcu)(&lh->gdev->srcu);

- if (!lh->gdev->chip)
+ if (!rcu_dereference(lh->gdev->chip))
return -ENODEV;

switch (cmd) {
@@ -1520,9 +1520,9 @@ static long linereq_ioctl(struct file *file, unsigned int cmd,
struct linereq *lr = file->private_data;
void __user *ip = (void __user *)arg;

- guard(rwsem_read)(&lr->gdev->sem);
+ guard(srcu)(&lr->gdev->srcu);

- if (!lr->gdev->chip)
+ if (!rcu_dereference(lr->gdev->chip))
return -ENODEV;

switch (cmd) {
@@ -1551,9 +1551,9 @@ static __poll_t linereq_poll(struct file *file,
struct linereq *lr = file->private_data;
__poll_t events = 0;

- guard(rwsem_read)(&lr->gdev->sem);
+ guard(srcu)(&lr->gdev->srcu);

- if (!lr->gdev->chip)
+ if (!rcu_dereference(lr->gdev->chip))
return EPOLLHUP | EPOLLERR;

poll_wait(file, &lr->wait, wait);
@@ -1573,9 +1573,9 @@ static ssize_t linereq_read(struct file *file, char __user *buf,
ssize_t bytes_read = 0;
int ret;

- guard(rwsem_read)(&lr->gdev->sem);
+ guard(srcu)(&lr->gdev->srcu);

- if (!lr->gdev->chip)
+ if (!rcu_dereference(lr->gdev->chip))
return -ENODEV;

if (count < sizeof(le))
@@ -1874,9 +1874,9 @@ static __poll_t lineevent_poll(struct file *file,
struct lineevent_state *le = file->private_data;
__poll_t events = 0;

- guard(rwsem_read)(&le->gdev->sem);
+ guard(srcu)(&le->gdev->srcu);

- if (!le->gdev->chip)
+ if (!rcu_dereference(le->gdev->chip))
return EPOLLHUP | EPOLLERR;

poll_wait(file, &le->wait, wait);
@@ -1912,9 +1912,9 @@ static ssize_t lineevent_read(struct file *file, char __user *buf,
ssize_t ge_size;
int ret;

- guard(rwsem_read)(&le->gdev->sem);
+ guard(srcu)(&le->gdev->srcu);

- if (!le->gdev->chip)
+ if (!rcu_dereference(le->gdev->chip))
return -ENODEV;

/*
@@ -1995,9 +1995,9 @@ static long lineevent_ioctl(struct file *file, unsigned int cmd,
void __user *ip = (void __user *)arg;
struct gpiohandle_data ghd;

- guard(rwsem_read)(&le->gdev->sem);
+ guard(srcu)(&le->gdev->srcu);

- if (!le->gdev->chip)
+ if (!rcu_dereference(le->gdev->chip))
return -ENODEV;

/*
@@ -2295,10 +2295,13 @@ static void gpio_v2_line_info_changed_to_v1(
static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
struct gpio_v2_line_info *info)
{
- struct gpio_chip *gc = desc->gdev->chip;
unsigned long dflags;
const char *label;

+ CLASS(gpio_chip_guard, guard)(desc);
+ if (!guard.gc)
+ return;
+
memset(info, 0, sizeof(*info));
info->offset = gpio_chip_hwgpio(desc);

@@ -2331,8 +2334,8 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
test_bit(FLAG_USED_AS_IRQ, &dflags) ||
test_bit(FLAG_EXPORT, &dflags) ||
test_bit(FLAG_SYSFS, &dflags) ||
- !gpiochip_line_is_valid(gc, info->offset) ||
- !pinctrl_gpio_can_use_line(gc, info->offset))
+ !gpiochip_line_is_valid(guard.gc, info->offset) ||
+ !pinctrl_gpio_can_use_line(guard.gc, info->offset))
info->flags |= GPIO_V2_LINE_FLAG_USED;

if (test_bit(FLAG_IS_OUT, &dflags))
@@ -2505,10 +2508,10 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
struct gpio_device *gdev = cdev->gdev;
void __user *ip = (void __user *)arg;

- guard(rwsem_read)(&gdev->sem);
+ guard(srcu)(&gdev->srcu);

/* We fail any subsequent ioctl():s when the chip is gone */
- if (!gdev->chip)
+ if (!rcu_dereference(gdev->chip))
return -ENODEV;

/* Fill in the struct and pass to userspace */
@@ -2591,9 +2594,9 @@ static __poll_t lineinfo_watch_poll(struct file *file,
struct gpio_chardev_data *cdev = file->private_data;
__poll_t events = 0;

- guard(rwsem_read)(&cdev->gdev->sem);
+ guard(srcu)(&cdev->gdev->srcu);

- if (!cdev->gdev->chip)
+ if (!rcu_dereference(cdev->gdev->chip))
return EPOLLHUP | EPOLLERR;

poll_wait(file, &cdev->wait, pollt);
@@ -2614,9 +2617,9 @@ static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
int ret;
size_t event_size;

- guard(rwsem_read)(&cdev->gdev->sem);
+ guard(srcu)(&cdev->gdev->srcu);

- if (!cdev->gdev->chip)
+ if (!rcu_dereference(cdev->gdev->chip))
return -ENODEV;

#ifndef CONFIG_GPIO_CDEV_V1
@@ -2691,10 +2694,10 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file)
struct gpio_chardev_data *cdev;
int ret = -ENOMEM;

- guard(rwsem_read)(&gdev->sem);
+ guard(srcu)(&gdev->srcu);

/* Fail on open if the backing gpiochip is gone */
- if (!gdev->chip)
+ if (!rcu_dereference(gdev->chip))
return -ENODEV;

cdev = kzalloc(sizeof(*cdev), GFP_KERNEL);
@@ -2781,6 +2784,7 @@ static const struct file_operations gpio_fileops = {

int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt)
{
+ struct gpio_chip *gc;
int ret;

cdev_init(&gdev->chrdev, &gpio_fileops);
@@ -2791,8 +2795,13 @@ int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt)
if (ret)
return ret;

- chip_dbg(gdev->chip, "added GPIO chardev (%d:%d)\n",
- MAJOR(devt), gdev->id);
+ guard(srcu)(&gdev->srcu);
+
+ gc = rcu_dereference(gdev->chip);
+ if (!gc)
+ return -ENODEV;
+
+ chip_dbg(gc, "added GPIO chardev (%d:%d)\n", MAJOR(devt), gdev->id);

return 0;
}
diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 2e3edf41e853..9f7b5e20fc25 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -171,6 +171,10 @@ static int gpio_sysfs_request_irq(struct device *dev, unsigned char flags)
unsigned long irq_flags;
int ret;

+ CLASS(gpio_chip_guard, guard)(desc);
+ if (!guard.gc)
+ return -ENODEV;
+
data->irq = gpiod_to_irq(desc);
if (data->irq < 0)
return -EIO;
@@ -195,7 +199,7 @@ static int gpio_sysfs_request_irq(struct device *dev, unsigned char flags)
* Remove this redundant call (along with the corresponding
* unlock) when those drivers have been fixed.
*/
- ret = gpiochip_lock_as_irq(desc->gdev->chip, gpio_chip_hwgpio(desc));
+ ret = gpiochip_lock_as_irq(guard.gc, gpio_chip_hwgpio(desc));
if (ret < 0)
goto err_put_kn;

@@ -209,7 +213,7 @@ static int gpio_sysfs_request_irq(struct device *dev, unsigned char flags)
return 0;

err_unlock:
- gpiochip_unlock_as_irq(desc->gdev->chip, gpio_chip_hwgpio(desc));
+ gpiochip_unlock_as_irq(guard.gc, gpio_chip_hwgpio(desc));
err_put_kn:
sysfs_put(data->value_kn);

@@ -225,9 +229,13 @@ static void gpio_sysfs_free_irq(struct device *dev)
struct gpiod_data *data = dev_get_drvdata(dev);
struct gpio_desc *desc = data->desc;

+ CLASS(gpio_chip_guard, guard)(desc);
+ if (!guard.gc)
+ return;
+
data->irq_flags = 0;
free_irq(data->irq, data);
- gpiochip_unlock_as_irq(desc->gdev->chip, gpio_chip_hwgpio(desc));
+ gpiochip_unlock_as_irq(guard.gc, gpio_chip_hwgpio(desc));
sysfs_put(data->value_kn);
}

@@ -444,13 +452,12 @@ static ssize_t export_store(const struct class *class,
const char *buf, size_t len)
{
struct gpio_desc *desc;
- struct gpio_chip *gc;
int status, offset;
long gpio;

status = kstrtol(buf, 0, &gpio);
- if (status < 0)
- goto done;
+ if (status)
+ return status;

desc = gpio_to_desc(gpio);
/* reject invalid GPIOs */
@@ -458,9 +465,13 @@ static ssize_t export_store(const struct class *class,
pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
return -EINVAL;
}
- gc = desc->gdev->chip;
+
+ CLASS(gpio_chip_guard, guard)(desc);
+ if (!guard.gc)
+ return -ENODEV;
+
offset = gpio_chip_hwgpio(desc);
- if (!gpiochip_line_is_valid(gc, offset)) {
+ if (!gpiochip_line_is_valid(guard.gc, offset)) {
pr_warn("%s: GPIO %ld masked\n", __func__, gpio);
return -EINVAL;
}
@@ -563,7 +574,6 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
const char *ioname = NULL;
struct gpio_device *gdev;
struct gpiod_data *data;
- struct gpio_chip *chip;
struct device *dev;
int status, offset;

@@ -578,16 +588,19 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
return -EINVAL;
}

+ CLASS(gpio_chip_guard, guard)(desc);
+ if (!guard.gc)
+ return -ENODEV;
+
if (!test_and_set_bit(FLAG_EXPORT, &desc->flags))
return -EPERM;

gdev = desc->gdev;
- chip = gdev->chip;

mutex_lock(&sysfs_lock);

/* check if chip is being removed */
- if (!chip || !gdev->mockdev) {
+ if (!gdev->mockdev) {
status = -ENODEV;
goto err_unlock;
}
@@ -606,14 +619,14 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)

data->desc = desc;
mutex_init(&data->mutex);
- if (chip->direction_input && chip->direction_output)
+ if (guard.gc->direction_input && guard.gc->direction_output)
data->direction_can_change = direction_may_change;
else
data->direction_can_change = false;

offset = gpio_chip_hwgpio(desc);
- if (chip->names && chip->names[offset])
- ioname = chip->names[offset];
+ if (guard.gc->names && guard.gc->names[offset])
+ ioname = guard.gc->names[offset];

dev = device_create_with_groups(&gpio_class, &gdev->dev,
MKDEV(0, 0), data, gpio_groups,
@@ -728,7 +741,7 @@ EXPORT_SYMBOL_GPL(gpiod_unexport);

int gpiochip_sysfs_register(struct gpio_device *gdev)
{
- struct gpio_chip *chip = gdev->chip;
+ struct gpio_chip *chip;
struct device *parent;
struct device *dev;

@@ -741,6 +754,12 @@ int gpiochip_sysfs_register(struct gpio_device *gdev)
if (!class_is_registered(&gpio_class))
return 0;

+ guard(srcu)(&gdev->srcu);
+
+ chip = rcu_dereference(gdev->chip);
+ if (!chip)
+ return -ENODEV;
+
/*
* For sysfs backward compatibility we need to preserve this
* preferred parenting to the gpio_chip parent field, if set.
@@ -767,7 +786,7 @@ int gpiochip_sysfs_register(struct gpio_device *gdev)
void gpiochip_sysfs_unregister(struct gpio_device *gdev)
{
struct gpio_desc *desc;
- struct gpio_chip *chip = gdev->chip;
+ struct gpio_chip *chip;

scoped_guard(mutex, &sysfs_lock) {
if (!gdev->mockdev)
@@ -779,6 +798,12 @@ void gpiochip_sysfs_unregister(struct gpio_device *gdev)
gdev->mockdev = NULL;
}

+ guard(srcu)(&gdev->srcu);
+
+ chip = rcu_dereference(gdev->chip);
+ if (chip)
+ return;
+
/* unregister gpiod class devices owned by sysfs */
for_each_gpio_desc_with_flag(chip, desc, FLAG_SYSFS) {
gpiod_unexport(desc);
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 9b1907f3e400..a14717a3e222 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,
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" : "",
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 35d71e30c546..b3810f7d286a 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -63,7 +63,7 @@ struct gpio_device {
int id;
struct device *mockdev;
struct module *owner;
- struct gpio_chip *chip;
+ struct gpio_chip __rcu *chip;
struct gpio_desc *descs;
int base;
u16 ngpio;
@@ -193,6 +193,26 @@ struct gpio_desc {

#define gpiod_not_found(desc) (IS_ERR(desc) && PTR_ERR(desc) == -ENOENT)

+struct gpio_chip_guard {
+ struct gpio_device *gdev;
+ struct gpio_chip *gc;
+ int idx;
+};
+
+DEFINE_CLASS(gpio_chip_guard,
+ struct gpio_chip_guard,
+ srcu_read_unlock(&_T.gdev->srcu, _T.idx),
+ ({
+ struct gpio_chip_guard _guard;
+
+ _guard.gdev = desc->gdev;
+ _guard.idx = srcu_read_lock(&_guard.gdev->srcu);
+ _guard.gc = rcu_dereference(_guard.gdev->chip);
+
+ _guard;
+ }),
+ struct gpio_desc *desc)
+
int gpiod_request(struct gpio_desc *desc, const char *label);
void gpiod_free(struct gpio_desc *desc);

--
2.40.1