Re: [PATCH v2 22/22] media: Ensure media device unregister is done only once
From: Mauro Carvalho Chehab <hidden>
Date: 2016-02-04 10:41:12
Also in:
alsa-devel, linux-media, lkml
Em Wed, 03 Feb 2016 21:03:54 -0700 Shuah Khan [off-list ref] escreveu:
media_device_unregister() checks if the media device is registered or not as the first step. However, the MEDIA_FLAG_REGISTERED bit doesn't get cleared until the end leaving a large window for two drivers to attempt media device unregister. The above leads to general protection faults when device is removed. Fix the problem with two phase media device unregister. Add a new interface media_devnode_start_unregister() to clear the MEDIA_FLAG_REGISTERED bit. Change media_device_unregister() call this interface to mark the start of unregister. This will ensure that media device unregister is done only once.
Hmm... it sounds simpler to use a kref at device register and when other drivers need instantiate media_dev. We can then do a kref_put() at unregister, and run the actual unregister code and media_ctl kfree only when kref is decremented on all drivers. Regards, Mauro
quoted hunk ↗ jump to hunk
Signed-off-by: Shuah Khan <redacted> --- drivers/media/media-device.c | 12 ++++++------ drivers/media/media-devnode.c | 15 ++++++++++----- include/media/media-devnode.h | 17 +++++++++++++++++ 3 files changed, 33 insertions(+), 11 deletions(-)diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c index 1f5d67e..584d46e 100644 --- a/drivers/media/media-device.c +++ b/drivers/media/media-device.c@@ -747,17 +747,17 @@ void media_device_unregister(struct media_device *mdev) struct media_entity *next; struct media_interface *intf, *tmp_intf; struct media_entity_notify *notify, *nextp; + int ret; if (mdev == NULL) return; - spin_lock(&mdev->lock); - - /* Check if mdev was ever registered at all */ - if (!media_devnode_is_registered(&mdev->devnode)) { - spin_unlock(&mdev->lock); + /* Start unregister - continue if necessary */ + ret = media_devnode_start_unregister(&mdev->devnode); + if (ret) return; - } + + spin_lock(&mdev->lock); /* Remove all entities from the media device */ list_for_each_entry_safe(entity, next, &mdev->entities, graph_obj.list)diff --git a/drivers/media/media-devnode.c b/drivers/media/media-devnode.c index 29409f4..c27f9e7 100644 --- a/drivers/media/media-devnode.c +++ b/drivers/media/media-devnode.c@@ -272,15 +272,20 @@ error: return ret; } -void media_devnode_unregister(struct media_devnode *mdev) +int __must_check media_devnode_start_unregister(struct media_devnode *mdev) { - /* Check if mdev was ever registered at all */ - if (!media_devnode_is_registered(mdev)) - return; - mutex_lock(&media_devnode_lock); + if (!media_devnode_is_registered(mdev)) { + mutex_unlock(&media_devnode_lock); + return -EINVAL; + } clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags); mutex_unlock(&media_devnode_lock); + return 0; +} + +void media_devnode_unregister(struct media_devnode *mdev) +{ device_unregister(&mdev->dev); }diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h index fe42f08..6f08677 100644 --- a/include/media/media-devnode.h +++ b/include/media/media-devnode.h@@ -120,6 +120,23 @@ int __must_check media_devnode_register(struct media_devnode *mdev, struct module *owner); /** + * media_devnode_start_unregister - start unregister on a media device node + * @mdev: the device node to start unregister + * + * This clears the MEDIA_FLAG_REGISTERED bit to indicate that unregister + * is in progress. + * + * This function can safely be called if the device node has never been + * registered or has already been unregistered. + * + * Zero is returned on success. + * + * -EINVAL is returned if the device node has never been + * registered or has already been unregistered. + */ +int __must_check media_devnode_start_unregister(struct media_devnode *mdev); + +/** * media_devnode_unregister - unregister a media device node * @mdev: the device node to unregister *