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    SubjectRe: Incorrect uses of get_driver()/put_driver()
    On Tue, Jan 10, 2012 at 10:05:41AM +0100, Martin Schwidefsky wrote:
    > On Mon, 9 Jan 2012 12:35:09 -0500 (EST)
    > Alan Stern <stern@rowland.harvard.edu> wrote:
    >
    > > drivers/s390/cio/device.c:1681: drv = get_driver(&cdrv->driver);
    > > drivers/s390/cio/device.c:1687: put_driver(drv);
    > >
    > > Martin, these calls seem to be useless. The calls in ccwgroup.c are
    > > definitely useless; there's no reason to take a reference to a driver
    > > while it's being unregistered, since it can't go away until the
    > > unregistration is finished.
    >
    > The get_driver/put_driver in ccwgroup.c are obviously useless, the caller
    > passed ccwgroup_driver_unregister a ccwgroup_driver reference.
    > I am not so sure about the code in device.c. get_ccwdev_by_busid() gets
    > used e.g. by vmur like this:

    It does not matter how it is being used. Either get_ccwdev_by_busid()
    gets a valid driver structure or you already lost. You can not say that
    get_driver() protects anything, since if there is a chance driver can
    disappear it can disappear before we get to executing get_driver() code.

    So while you might want to audit callers get/put_driver inside of
    get_ccwdev_by_busid() is utterly useless.

    Thanks.

    --
    Dmitry


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