counter: Provide alternative counter registration functions

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.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211230150300.72196-14-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/include/linux/counter.h b/include/linux/counter.h
index 627f1757f6bb..ed8d5820f0d1 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);