Commit 799a66ba authored Nov 08, 2013 by Ian Abbott Committed by Greg Kroah-Hartman Nov 11, 2013

staging: comedi: kcomedilib: increment reference while device in use



Low-level comedi drivers that use the "kcomedilib" module (currently only
the "comedi_bond" driver) call `comedi_open()` to "open" another comedi
device (not as a file) and `comedi_close()` to "close" it.  (Note: these
are the functions exported by the "kcomedilib" module, not the
identically named, statically linked functions in the core "comedi"
module.)

In `comedi_open()`, call `comedi_dev_get_from_minor()` instead of
`comedi_dev_from_minor()` to get the pointer to the `struct
comedi_device` being "opened".  This increments its reference count to
prevent it being freed.  Call `comedi_dev_put()` if `comedi_open()`
returns `NULL`, and also call it from `comedi_close()`.  This decrements
the reference count.

Note that although we now protect against the `struct comedi_device`
being freed, we do not yet protect against it being "detached" while it
is being used.  This will be addressed by a later patch.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent be535c9a

drivers/staging/comedi/kcomedilib/kcomedilib_main.c

+12 −7

Original line number	Diff line number	Diff line
		@@ -35,7 +35,7 @@ MODULE_LICENSE("GPL");

		struct comedi_device comedi_open(const char filename)
		{
		struct comedi_device *dev;
		struct comedi_device dev, retval = NULL;
		unsigned int minor;

		if (strncmp(filename, "/dev/comedi", 11) != 0)
		@@ -46,15 +46,19 @@ struct comedi_device comedi_open(const char filename)
		if (minor >= COMEDI_NUM_BOARD_MINORS)
		return NULL;

		dev = comedi_dev_from_minor(minor);

		if (!dev \|\| !dev->attached)
		dev = comedi_dev_get_from_minor(minor);
		if (!dev)
		return NULL;

		if (!try_module_get(dev->driver->module))
		return NULL;
		if (dev->attached && try_module_get(dev->driver->module))
		retval = dev;
		else
		retval = NULL;

		if (retval == NULL)
		comedi_dev_put(dev);

		return dev;
		return retval;
		}
		EXPORT_SYMBOL_GPL(comedi_open);

		@@ -63,6 +67,7 @@ int comedi_close(struct comedi_device *d)
		struct comedi_device dev = (struct comedi_device )d;

		module_put(dev->driver->module);
		comedi_dev_put(dev);

		return 0;
		}