staging:iio:core set the iio_dev.info pointer to null on unregister u…

…nder lock.

This prevents use of provider callbacks after it has been unregistered.
Note that all code using this that can be called from a consumer *must*
check the pointer before using and hold the info_exist_lock throughout
the usage of the callbacks in info.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/iio.h

@@ -310,6 +310,7 @@ struct iio_buffer_setup_ops {
  * @chan_attr_group:	[INTERN] group for all attrs in base directory
  * @name:		[DRIVER] name of the device.
  * @info:		[DRIVER] callbacks and constant info from driver
+ * @info_exist_lock:	[INTERN] lock to prevent use during removal
  * @chrdev:		[INTERN] associated character device
  * @groups:		[INTERN] attribute groups
  * @groupcounter:	[INTERN] index of next attribute group
@@ -340,6 +341,7 @@ struct iio_dev {
 	struct attribute_group		chan_attr_group;
 	const char			*name;
 	const struct iio_info		*info;
+	struct mutex			info_exist_lock;
 	const struct iio_buffer_setup_ops	*setup_ops;
 	struct cdev			chrdev;
 #define IIO_MAX_GROUPS 6

drivers/staging/iio/industrialio-core.c

@@ -594,6 +594,7 @@ struct iio_dev *iio_allocate_device(int sizeof_priv)
 		device_initialize(&dev->dev);
 		dev_set_drvdata(&dev->dev, (void *)dev);
 		mutex_init(&dev->mlock);
+		mutex_init(&dev->info_exist_lock);
 
 		dev->id = ida_simple_get(&iio_ida, 0, 0, GFP_KERNEL);
 		if (dev->id < 0) {
@@ -718,6 +719,9 @@ EXPORT_SYMBOL(iio_device_register);
 
 void iio_device_unregister(struct iio_dev *indio_dev)
 {
+	mutex_lock(&indio_dev->info_exist_lock);
+	indio_dev->info = NULL;
+	mutex_unlock(&indio_dev->info_exist_lock);
 	device_unregister(&indio_dev->dev);
 }
 EXPORT_SYMBOL(iio_device_unregister);