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Message-ID: <56B255D6.9080908@osg.samsung.com>
Date: Wed, 3 Feb 2016 12:32:38 -0700
From: Shuah Khan <shuahkh@....samsung.com>
To: Mauro Carvalho Chehab <mchehab@....samsung.com>
Cc: tiwai@...e.com, clemens@...isch.de, hans.verkuil@...co.com,
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linux-media@...r.kernel.org, linux-api@...r.kernel.org,
alsa-devel@...a-project.org, Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH 29/31] media: track media device unregister in progress
On 01/28/2016 01:42 PM, Shuah Khan wrote:
> On 01/28/2016 10:28 AM, Mauro Carvalho Chehab wrote:
>> Em Thu, 28 Jan 2016 10:04:24 -0700
>> Shuah Khan <shuahkh@....samsung.com> escreveu:
>>
>>> On 01/28/2016 10:01 AM, Mauro Carvalho Chehab wrote:
>>>> Em Wed, 6 Jan 2016 13:27:18 -0700
>>>> Shuah Khan <shuahkh@....samsung.com> escreveu:
>>>>
>>>>> 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().
>>
>> I guess the call to:
>> device_remove_file(&mdev->devnode.dev, &dev_attr_model);
>>
>> IMO, This should be, instead, at media_devnode_unregister().
>>
>> Then, we can change the logic at media_devnode_unregister() to:
>>
>> void media_devnode_unregister(struct media_devnode *mdev)
>> {
>> mutex_lock(&media_devnode_lock);
>>
>> /* Check if mdev was ever registered at all */
>> if (!media_devnode_is_registered(mdev)) {
>> mutex_unlock(&media_devnode_lock);
>> return;
>> }
>>
>> clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
>> mutex_unlock(&media_devnode_lock);
>> device_remove_file(&mdev->devnode.dev, &dev_attr_model);
>> device_unregister(&mdev->dev);
>> }
>>
>> This sounds enough to avoid device_unregister() or device_remove_file()
>> to be called twice.
>>
>
> I can give it a try. There might other problems that could
> result from media device being a devres in this case. The
> last put_device on the usbdev parent device (media device
> is created as devres for this), all device resources get
> released. That might have to be solved in a different way.
>
> For now I will see if your solution works.
Hi Mauro,
Moving device_remove_file() won't be easy without
making more changes. The file is created in
media_device_regsiter() and all the attributes are
handled in media-device.c
One solution I can think of is clearing the
MEDIA_FLAG_REGISTERED bit very early in
media_device_unregister()
--- a/drivers/media/media-device.c
+++ b/drivers/media/media-device.c
@@ -759,6 +759,9 @@ void media_device_unregister(struct media_device *mdev)
return;
}
+ /* Protect unregister path - clear MEDIA_FLAG_REGISTERED */
+ clear_bit(MEDIA_FLAG_REGISTERED, &mdev->devnode.flags);
+
/* Remove all entities from the media device */
list_for_each_entry_safe(entity, next, &mdev->entities, graph_obj.list)
__media_device_unregister_entity(entity);
and changing media_devnode_unregister() to simply call
device_unregister(&mdev->dev);
Again clearing MEDIA_FLAG_REGISTERED bit in
media_device_unregister() some problems.
For one thing clearing this bit should be
done holding media_devnode_lock. It can be
done cleanly if we do the following:
How about if we split media_devnode_unregister()
into twp ohases:
media_devnode_start_unregister()
to clear this bit. It can do:
media_devnode_start_unregister()
{
mutex_lock(&media_devnode_lock);
if (!media_devnode_is_registered(mdev)) {
mutex_unlock(&media_devnode_lock);
return;
}
clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
mutex_unlock(&media_devnode_lock);
}
then:media_device_unregister(struct media_device *mdev)
will call this first thing and then hold mdev->lock
do the rest and the call media_devnode_unregister()
and which will be changed to as follows:
--- a/drivers/media/media-devnode.c
+++ b/drivers/media/media-devnode.c
@@ -274,13 +274,6 @@ error:
void media_devnode_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);
- clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
- mutex_unlock(&media_devnode_lock);
device_unregister(&mdev->dev);
}
thanks,
-- Shuah
--
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@....samsung.com | (970) 217-8978
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