[RESEND PATCH] iio: core: Fix double free.

[Martin Fuzzey <mfuzzey@parkeon.com>]

When an error occurred during event registration memory was freed twice
resulting in kernel memory corruption and a crash in unrelated code.

The problem was caused by
	iio_device_unregister_eventset()
	iio_device_unregister_sysfs()

being called twice, once on the error path and then
again via iio_dev_release().

Fix this by making these two functions idempotent so they
may be called multiple times.

The problem was observed before applying
	78b33216 iio:core: Handle error when mask type is not separate

Signed-off-by: Martin Fuzzey <mfuzzey@parkeon.com>
---
 drivers/iio/industrialio-core.c  |    5 +++--
 drivers/iio/industrialio-event.c |    1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index af3e76d..f009d05 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -832,8 +832,7 @@ static int iio_device_add_channel_sysfs(struct iio_dev *indio_dev,
  * @attr_list: List of IIO device attributes
  *
  * This function frees the memory allocated for each of the IIO device
- * attributes in the list. Note: if you want to reuse the list after calling
- * this function you have to reinitialize it using INIT_LIST_HEAD().
+ * attributes in the list.
  */
 void iio_free_chan_devattr_list(struct list_head *attr_list)
 {
@@ -841,6 +840,7 @@ void iio_free_chan_devattr_list(struct list_head *attr_list)
 
 	list_for_each_entry_safe(p, n, attr_list, l) {
 		kfree(p->dev_attr.attr.name);
+		list_del(&p->l);
 		kfree(p);
 	}
 }
@@ -921,6 +921,7 @@ static void iio_device_unregister_sysfs(struct iio_dev *indio_dev)
 
 	iio_free_chan_devattr_list(&indio_dev->channel_attr_list);
 	kfree(indio_dev->chan_attr_group.attrs);
+	indio_dev->chan_attr_group.attrs = NULL;
 }
 
 static void iio_dev_release(struct device *device)
diff --git a/drivers/iio/industrialio-event.c b/drivers/iio/industrialio-event.c
index 0c1e37e..35c02ae 100644
--- a/drivers/iio/industrialio-event.c
+++ b/drivers/iio/industrialio-event.c
@@ -493,6 +493,7 @@ int iio_device_register_eventset(struct iio_dev *indio_dev)
 error_free_setup_event_lines:
 	iio_free_chan_devattr_list(&indio_dev->event_interface->dev_attr_list);
 	kfree(indio_dev->event_interface);
+	indio_dev->event_interface = NULL;
 	return ret;
 }