On 01/28/2016 10:01 AM, Mauro Carvalho Chehab wrote:

Em Wed,  6 Jan 2016 13:27:18 -0700
Shuah Khan [off-list ref] escreveu:

quoted

Add support to track media device unregister in progress
state to prevent more than one driver entering unregister.
This enables fixing the general protection faults while
snd-usb-audio was cleaning up media resources for pcm
streams and mixers. In this patch a new interface is added
to return the unregister in progress state. Subsequent
patches to snd-usb-audio and au0828-core use this interface
to avoid entering unregister and attempting to unregister
entities and remove devnodes while unregister is in progress.
Media device unregister removes entities and interface nodes.

Hmm... isn't the spinlock enough to serialize it? It seems weird the
need of an extra bool here to warrant that this is really serialized.

The spinlock and check for media_devnode_is_registered(&mdev->devnode)
aren't enough to ensure only one driver enters the unregister. Please
note that the devnode isn't marked unregistered until the end in
media_device_unregister().

quoted

Signed-off-by: Shuah Khan <redacted>
---
 drivers/media/media-device.c |  5 ++++-
 include/media/media-device.h | 17 +++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
index 20c85a9..1bb9a5f 100644
--- a/drivers/media/media-device.c
+++ b/drivers/media/media-device.c

@@ -749,10 +749,13 @@ void media_device_unregister(struct media_device *mdev)
 	spin_lock(&mdev->lock);
 
 	/* Check if mdev was ever registered at all */
-	if (!media_devnode_is_registered(&mdev->devnode)) {
+	/* check if unregister is in progress */
+	if (!media_devnode_is_registered(&mdev->devnode) ||
+	    mdev->unregister_in_progress) {
 		spin_unlock(&mdev->lock);
 		return;
 	}
+	mdev->unregister_in_progress = true;
 
 	/* Remove all entities from the media device */
 	list_for_each_entry_safe(entity, next, &mdev->entities, graph_obj.list)

diff --git a/include/media/media-device.h b/include/media/media-device.h
index 04b6c2e..0807292 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h

@@ -332,6 +332,10 @@ struct media_device {
 	spinlock_t lock;
 	/* Serializes graph operations. */
 	struct mutex graph_mutex;
+	/* Tracks unregister in progress state to prevent
+	 * more than one driver entering unregister
+	*/
+	bool unregister_in_progress;
 
 	/* Handlers to find source entity for the sink entity and
 	 * check if it is available, and activate the link using

@@ -365,6 +369,7 @@ struct media_device {
 /* media_devnode to media_device */
 #define to_media_device(node) container_of(node, struct media_device, devnode)
 
+
 /**
  * media_entity_enum_init - Initialise an entity enumeration
  *

@@ -553,6 +558,12 @@ struct media_device *media_device_get_devres(struct device *dev);
  * @dev: pointer to struct &device.
  */
 struct media_device *media_device_find_devres(struct device *dev);
+/* return unregister in progress state */
+static inline bool media_device_is_unregister_in_progress(
+					struct media_device *mdev)
+{
+	return mdev->unregister_in_progress;
+}
 
 /* Iterate over all entities. */
 #define media_device_for_each_entity(entity, mdev)			\

@@ -569,6 +580,7 @@ struct media_device *media_device_find_devres(struct device *dev);
 /* Iterate over all links. */
 #define media_device_for_each_link(link, mdev)			\
 	list_for_each_entry(link, &(mdev)->links, graph_obj.list)
+
 #else
 static inline int media_device_register(struct media_device *mdev)
 {

@@ -604,5 +616,10 @@ static inline struct media_device *media_device_find_devres(struct device *dev)
 {
 	return NULL;
 }
+static inline bool media_device_is_unregister_in_progress(
+					struct media_device *mdev)
+{
+	return false;
+}
 #endif /* CONFIG_MEDIA_CONTROLLER */
 #endif

-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978