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    SubjectRe: kobject_put vs module unload
    On Sat, Jan 8, 2011 at 19:01, Mikulas Patocka <mpatocka@redhat.com> wrote:
    > On Sat, 8 Jan 2011, Kay Sievers wrote:
    >> On Sat, Jan 8, 2011 at 14:19, Mikulas Patocka <mpatocka@redhat.com> wrote:
    >> > On Fri, 7 Jan 2011, Greg KH wrote:
    >>
    >> >> > 4) the reference obtained at point 1) is dropped, kobject reference count
    >> >> > reaches zero and the release callback is called. But that callback points
    >> >> > to an unloaded module and causes a crash.
    >> >> >
    >> >> > How is it solved? Am I missing something?
    >> >>
    >> >> You have the code that creates and frees the object, to not be in the
    >> >> module that could have been unloaded.  It's really just that simple.
    >> >
    >> > If the whole device mapper subsystem can be a module, where can I put the
    >> > code?
    >> >
    >> > I think a similar bug exists in md, it can also be unloaded as a module
    >> > and it has "release" method in its module code.
    >>
    >> If you still have data structures hanging around, these structures are
    >> supposed to take a reference on the module -- and you can not unload
    >> the module as long as this is the case.
    >>
    >> Kay
    >
    > kobject references don't increase module reference count. If kobject held
    > module references, it would be a fix for this bug, but could cause other
    > bugs (some modules could be unloadable due to self-references to its own
    > kobjects).

    Sure, they don't automatically take references. It's the job of the
    driver/module, to make sure to pin the module for any data of it,
    which might be still in use.

    Kay
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