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SubjectRe: [PATCH v2 13/23] counter: Provide alternative counter registration functions
On Mon, Dec 27, 2021 at 10:45:16AM +0100, Uwe Kleine-König wrote:
> The current implementation gets device lifetime tracking wrong. The
> problem is that allocation of struct counter_device is controlled by the
> individual drivers but this structure contains a struct device that
> might have to live longer than a driver is bound. As a result a command
> sequence like:
>
> { sleep 5; echo bang; } > /dev/counter0 &
> sleep 1;
> echo 40000000.timer:counter > /sys/bus/platform/drivers/stm32-timer-counter/unbind
>
> can keep a reference to the struct device and unbinding results in
> freeing the memory occupied by this device resulting in an oops.
>
> This commit provides two new functions (plus some helpers):
> - counter_alloc() to allocate a struct counter_device that is
> automatically freed once the embedded struct device is released
> - counter_add() to register such a device.
>
> Note that this commit doesn't fix any issues, all drivers have to be
> converted to these new functions to correct the lifetime problems.
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

I agree with the approach taken in this patch, and I don't have much to
add after the suggestions Lars-Peter and Jonathan have already given. So
assuming those are addressed in the next version I expect to Ack this
patch as well.

> ---
> drivers/counter/counter-core.c | 149 ++++++++++++++++++++++++++++++++-
> include/linux/counter.h | 15 ++++
> 2 files changed, 163 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/counter/counter-core.c b/drivers/counter/counter-core.c
> index 00c41f28c101..8261567b6272 100644
> --- a/drivers/counter/counter-core.c
> +++ b/drivers/counter/counter-core.c
> @@ -15,6 +15,7 @@
> #include <linux/kdev_t.h>
> #include <linux/module.h>
> #include <linux/mutex.h>
> +#include <linux/slab.h>
> #include <linux/types.h>
> #include <linux/wait.h>
>
> @@ -24,6 +25,11 @@
> /* Provides a unique ID for each counter device */
> static DEFINE_IDA(counter_ida);
>
> +struct counter_device_allochelper {
> + struct counter_device counter;
> + unsigned long privdata[];
> +};
> +
> static void counter_device_release(struct device *dev)
> {
> struct counter_device *const counter =
> @@ -31,6 +37,9 @@ static void counter_device_release(struct device *dev)
>
> counter_chrdev_remove(counter);
> ida_free(&counter_ida, dev->id);
> +
> + if (!counter->legacy_device)
> + kfree(container_of(counter, struct counter_device_allochelper, counter));
> }
>
> static struct device_type counter_device_type = {
> @@ -53,7 +62,14 @@ static dev_t counter_devt;
> */
> void *counter_priv(const struct counter_device *const counter)
> {
> - return counter->priv;
> + if (counter->legacy_device) {
> + return counter->priv;
> + } else {
> + struct counter_device_allochelper *ch =
> + container_of(counter, struct counter_device_allochelper, counter);
> +
> + return &ch->privdata;
> + }
> }
> EXPORT_SYMBOL_GPL(counter_priv);
>
> @@ -74,6 +90,8 @@ int counter_register(struct counter_device *const counter)
> int id;
> int err;
>
> + counter->legacy_device = true;
> +
> /* Acquire unique ID */
> id = ida_alloc(&counter_ida, GFP_KERNEL);
> if (id < 0)
> @@ -114,6 +132,100 @@ int counter_register(struct counter_device *const counter)
> }
> EXPORT_SYMBOL_GPL(counter_register);
>
> +/**
> + * counter_alloc - allocate a counter_device
> + * @sizeof_priv: size of the driver private data
> + *
> + * This is part one of counter registration. The structure is allocated
> + * dynamically to ensure the right lifetime for the embedded struct device.
> + *
> + * If this succeeds, call counter_put() to get rid of the counter_device again.
> + */
> +struct counter_device *counter_alloc(size_t sizeof_priv)
> +{
> + struct counter_device_allochelper *ch;
> + struct counter_device *counter;
> + struct device *dev;
> + int id, err;
> +
> + ch = kzalloc(sizeof(*ch) + sizeof_priv, GFP_KERNEL);
> + if (!ch) {
> + err = -ENOMEM;
> + goto err_alloc_ch;
> + }
> +
> + counter = &ch->counter;
> + dev = &counter->dev;
> +
> + /* Acquire unique ID */
> + err = ida_alloc(&counter_ida, GFP_KERNEL);
> + if (err < 0) {
> + goto err_ida_alloc;
> + }
> + dev->id = err;
> +
> + err = counter_chrdev_add(counter);
> + if (err < 0)
> + goto err_chrdev_add;
> +
> + device_initialize(dev);
> + /* Configure device structure for Counter */
> + dev->type = &counter_device_type;
> + dev->bus = &counter_bus_type;
> + dev->devt = MKDEV(MAJOR(counter_devt), id);
> +
> + mutex_init(&counter->ops_exist_lock);
> +
> + return counter;
> +
> +err_chrdev_add:
> +
> + ida_free(&counter_ida, dev->id);
> +err_ida_alloc:
> +
> + kfree(ch);
> +err_alloc_ch:
> +
> + return ERR_PTR(err);
> +}
> +EXPORT_SYMBOL_GPL(counter_alloc);
> +
> +void counter_put(struct counter_device *counter)
> +{
> + put_device(&counter->dev);
> +}
> +
> +/**
> + * counter_add - complete registration of a counter
> + * @counter: the counter to add
> + *
> + * This is part two of counter registration.
> + *
> + * If this succeeds, call counter_unregister() to get rid of the counter_device again.
> + */
> +int counter_add(struct counter_device *counter)
> +{
> + int err;
> + struct device *dev = &counter->dev;
> +
> + get_device(&counter->dev);
> +
> + if (counter->parent) {
> + dev->parent = counter->parent;
> + dev->of_node = counter->parent->of_node;
> + }
> +
> + err = counter_sysfs_add(counter);
> + if (err < 0)
> + return err;
> +
> + /* implies device_add(dev) */
> + err = cdev_device_add(&counter->chrdev, dev);
> +
> + return err;
> +}
> +EXPORT_SYMBOL_GPL(counter_add);
> +
> /**
> * counter_unregister - unregister Counter from the system
> * @counter: pointer to Counter to unregister
> @@ -168,6 +280,41 @@ int devm_counter_register(struct device *dev,
> }
> EXPORT_SYMBOL_GPL(devm_counter_register);
>
> +static void devm_counter_put(void *counter)
> +{
> + counter_put(counter);
> +}
> +
> +struct counter_device *devm_counter_alloc(struct device *dev, size_t sizeof_priv)
> +{
> + struct counter_device *counter;
> + int err;
> +
> + counter = counter_alloc(sizeof_priv);
> + if (IS_ERR(counter))
> + return counter;
> +
> + err = devm_add_action_or_reset(dev, devm_counter_put, counter);
> + if (err < 0)
> + return ERR_PTR(err);
> +
> + return counter;
> +}
> +EXPORT_SYMBOL_GPL(devm_counter_alloc);
> +
> +int devm_counter_add(struct device *dev,
> + struct counter_device *const counter)
> +{
> + int err;
> +
> + err = counter_add(counter);
> + if (err < 0)
> + return err;
> +
> + return devm_add_action_or_reset(dev, devm_counter_release, counter);
> +}
> +EXPORT_SYMBOL_GPL(devm_counter_add);
> +
> #define COUNTER_DEV_MAX 256
>
> static int __init counter_init(void)
> diff --git a/include/linux/counter.h b/include/linux/counter.h
> index 8daaa38c71d8..f1350a43cd48 100644
> --- a/include/linux/counter.h
> +++ b/include/linux/counter.h
> @@ -327,14 +327,29 @@ struct counter_device {
> spinlock_t events_in_lock;
> struct mutex events_out_lock;
> struct mutex ops_exist_lock;
> +
> + /*
> + * This can go away once all drivers are converted to
> + * counter_alloc()/counter_add().
> + */
> + bool legacy_device;
> };
>
> void *counter_priv(const struct counter_device *const counter);
>
> int counter_register(struct counter_device *const counter);
> +
> +struct counter_device *counter_alloc(size_t sizeof_priv);
> +void counter_put(struct counter_device *const counter);
> +int counter_add(struct counter_device *const counter);
> +
> void counter_unregister(struct counter_device *const counter);
> int devm_counter_register(struct device *dev,
> struct counter_device *const counter);
> +struct counter_device *devm_counter_alloc(struct device *dev,
> + size_t sizeof_priv);
> +int devm_counter_add(struct device *dev,
> + struct counter_device *const counter);
> void counter_push_event(struct counter_device *const counter, const u8 event,
> const u8 channel);
>
> --
> 2.33.0
>
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