[lkml]   [2012]   [Jan]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Public ridicule due to sound/soc/soc-core.c abuse of the driver model
On Fri, Jan 06, 2012 at 12:15:01PM -0800, Mark Brown wrote:
> On Fri, Jan 06, 2012 at 11:40:52AM -0800, Greg KH wrote:
> > It was recently pointed out to me that the sound/soc/soc-core.c is
> > flagrantly abusing the driver model by providing "empty" release
> > functions, just to keep the kernel from complaining:
> > Come on people, do you think that I wrote the code in the kernel that
> > produces those errors just for fun? It was telling you to fix your code
> > by providing a function to free the structure that is being released,
> > not to try to trick the kernel because you think you know better. The
> > kernel was trying to help you out here, to get the programming model
> > correct, in a place that was commonly misunderstood.
> The problem is that due to the entertaining nature of AC'97 support in
> Linux we don't actually have anything to free at this point - we'd need
> to redo the whole infrastructure, not just this code.

The fact is that these bugs are oopses waiting to happen. All you need
is the kernel to hold a reference to the kobject underlying the struct
device, and then release that reference after you've kfree'd the structure
containing the struct device, and the kernel will go bang.

I also disagree with your statement - I think it's quite simple to fix:

1. Change to using a flag to indicate whether the struct device is
registered rather than ac97->dev.bus.
2. Change snd_soc_new_ac97_codec() to initialize codec->ac97->dev,
including calling device_initialize() on it and setting the release
3. Change device_register(&codec->ac97->dev); to
4. Make the AC97 device release function do the freeing of 'codec->ac97'
5. Change the current device_unregister(&codec->ac97->dev); to
6. Change the various kfree(codec->ac97); in the file to do a

This will cause device_put() to check the refcount, when that hits
zero it will call the release function, and that in turn will then
kfree() the ac97 structure.

If someone else is holding a reference to this struct device, kfree
will be called once that reference is dropped - and this is the
exact behaviour the driver model as a whole requires.

At least this gets the AC97 ASoC stuff fixed, and one less abuse of the
driver model in the kernel.

 \ /
  Last update: 2012-01-06 21:53    [W:1.255 / U:2.020 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site