[PATCH v3 13/23] counter: Provide alternative counter registration functions

Uwe Kleine-König
2021-12-29T15:45:24Z

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>
---
drivers/counter/counter-core.c | 168 ++++++++++++++++++++++++++++++++-
include/linux/counter.h | 15 +++
2 files changed, 181 insertions(+), 2 deletions(-)

diff --git a/drivers/counter/counter-core.c b/drivers/counter/counter-core.c
index 00c41f28c101..b3fa15bbcbdb 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 +25,16 @@
/* Provides a unique ID for each counter device */
static DEFINE_IDA(counter_ida);

+struct counter_device_allochelper {
+ struct counter_device counter;
+
+ /*
+ * This is cache line aligned to ensure private data behaves like if it
+ * were kmalloced separately.
+ */
+ unsigned long privdata[] ____cacheline_aligned;
+};
+
static void counter_device_release(struct device *dev)
{
struct counter_device *const counter =
@@ -31,6 +42,9 @@ 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 +67,14 @@ 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 +95,8 @@ 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 +137,95 @@ 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 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;
+
+ mutex_init(&counter->ops_exist_lock);
+ dev->type = &counter_device_type;
+ dev->bus = &counter_bus_type;
+ dev->devt = MKDEV(MAJOR(counter_devt), dev->id);
+
+ err = counter_chrdev_add(counter);
+ if (err < 0)
+ goto err_chrdev_add;
+
+ device_initialize(dev);
+
+ 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);
+}
+EXPORT_SYMBOL_GPL(counter_put);
+
+/**
+ * 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;
+
+ 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) */
+ return cdev_device_add(&counter->chrdev, dev);
+}
+EXPORT_SYMBOL_GPL(counter_add);
+
/**
* counter_unregister - unregister Counter from the system
* @counter: pointer to Counter to unregister
@@ -134,7 +246,8 @@ void counter_unregister(struct counter_device *const counter)

mutex_unlock(&counter->ops_exist_lock);

- put_device(&counter->dev);
+ if (counter->legacy_device)
+ put_device(&counter->dev);
}
EXPORT_SYMBOL_GPL(counter_unregister);

@@ -168,6 +281,57 @@ int devm_counter_register(struct device *dev,
}
EXPORT_SYMBOL_GPL(devm_counter_register);

+static void devm_counter_put(void *counter)
+{
+ counter_put(counter);
+}
+
+/**
+ * devm_counter_alloc - allocate a counter_device
+ * @dev: the device to register the release callback for
+ * @sizeof_priv: size of the driver private data
+ *
+ * This is the device managed version of counter_add(). It registers a cleanup
+ * callback to care for calling counter_put().
+ */
+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);
+
+/**
+ * devm_counter_add - complete registration of a counter
+ * @dev: the device to register the release callback for
+ * @counter: the counter to add
+ *
+ * This is the device managed version of counter_add(). It registers a cleanup
+ * callback to care for calling counter_unregister().
+ */
+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);

--
2.34.1