staging/comedi: keep reference to class device after destroyed
authorIan Abbott <abbotti@mev.co.uk>
Wed, 11 Dec 2013 14:51:02 +0000 (14:51 +0000)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Tue, 17 Dec 2013 21:09:43 +0000 (13:09 -0800)
commit8f988d8784e3fa4bb50dabeec516cd3fbdb4ea73
treef211190884237decdecc0e1715b37343bc877369
parenta3b22220a48bd14c9ba4ca8d051b0c92d5bc3866
staging/comedi: keep reference to class device after destroyed

When a dynamically allocated `struct comedi_device` gets automatically
unconfigured by a call to `comedi_auto_unconfig()` from a lower-level
driver's bus removal function (e.g. when a USB device is disconnected),
the class device in `dev->class_dev` (where `dev` points to the `struct
comedi_device`) is destroyed by a call to `device_destroy()` that
matches a previous call to `device_create()`.

However, if the `struct comedi_device` is still associated with an open
file object, the now invalid `dev->class_dev` pointer may still be
passed to `dev_printk()` (via `dev_dbg()` etc.), producing bogus output
or worse.

To fix this, call `get_device()` on the class device if
`device_create()` was successful.  Add a matching call to `put_device()`
in `comedi_dev_kref_release()` when the `struct comedi_device` is freed.
The calls to `dev_dbg()` etc. after the call to `device_destroy()` will
still produce valid output, although the device will have been
unregistered in sysfs.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/staging/comedi/comedi_fops.c