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    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:0.021 / U:0.040 seconds]
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