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    SubjectRe: [RFC] Input: Remove unsafe device module references
    On Tue, Nov 01, 2011 at 10:52:10AM -0700, Dmitry Torokhov wrote:
    > On Tue, Nov 01, 2011 at 10:01:56AM -0700, Greg KH wrote:
    > > On Tue, Nov 01, 2011 at 04:41:40PM +0100, David Herrmann wrote:
    > > > Hi Dmitry and Greg
    > > >
    > > > It doesn't make sense to take a reference to our own module. When we call
    > > > module_put(THIS_MODULE) we cannot make sure that our module is still alive when
    > > > this function returns. Therefore, module_put() will return to invalid memory and
    > > > our input_dev_release() function is no longer available.
    > > >
    > > > It would be interesting if Greg could elaborate what else we could do to replace
    > > > this module-refcount as it is definitely needed here. However, "struct device"
    > > > doesn't provide an owner field so there is no way for us to let the device core
    > > > keep a reference to our module.
    > >
    > > For a bus module, yes, this is needed, so don't remove these calls, it's
    > > wrong to do so.
    >
    > Strictly speaking, David is right, there is a race condition here.
    > However since we do module_put() as very last operation of
    > input_dev_release() it is extremely hard to trigger this race.
    >
    > Until we have a better way of pinning the bus (or class) implementation
    > in memory we should keep __module_get/module_put in input core.

    I agree, that's fine for a bus to do, as long as you are aware of how it
    is working.

    greg k-h


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