Re: [PATCH 5/8] [media] em28xx: initial support for HAUPPAUGE HVR-930C again

[Mark Lord <kernel@teksavvy.com>]

On 11-12-06 08:56 AM, Devin Heitmueller wrote:
> On Tue, Dec 6, 2011 at 8:43 AM, Mauro Carvalho Chehab
> <mchehab@redhat.com> wrote:
>> The driver who binds everything is the bridge driver. In your case, it is
>> the au0828 driver.
>>
>> What you're experiencing seems to be some race issue inside it, and not at
>> xc5000.
>>
>> On a quick look on it, I'm noticing that there's no lock at
>> au0828_usb_probe().
>>
>> Also, it uses a separate lock for analog and for digital:
>>
>>        mutex_init(&dev->mutex);
>>        mutex_init(&dev->dvb.lock);
>>
>> Probably, the right thing to do would be to use just one lock for both
>> rising
>> it at usb_probe, lowering it just before return 0. This will avoid any open
>> operations while the device is not fully initialized. Btw, newer udev's open
>> the analog part of the driver just after V4L register, in order to get the
>> device capabilities. This is known to cause race conditions, if the locking
>> schema is not working properly.
> 
> Just to be clear, we're now talking about a completely different race
> condition that has nothing to do with the subject at hand, and this
> discussion should probably be moved to a new thread.

If this discussion does change threads, could you folks please copy me
on it?  I'm already subscribed to several other kernel mailing lists
in my roles as developer and maintainer of various bits, but I would
like to avoid having yet another daily deluge added to my inbox.  :)

That said, I can test possible fixes for this stuff,
and am rather interested to see it resolved.
..
> The notion that this is something that has been there for over a year
> is something I only learned of in the last couple of days.  All the
> complaints I had seen thus far were from existing users who were
> perfectly happy until they upgraded their kernel a couple of months
> ago and then started seeing the problem.
..

It's always exhibited races for me here.  I have long since worked around
the issue(s), so my own systems currently behave.   But with the newer
HVR-950Q revision (B4F0), the issue is far more prevalent than before.

I may try Mauro's locking suggestion -- more detail or a patch would be useful.

Mauro?