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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>
This commit is contained in:
Ian Abbott 2013-11-08 15:03:38 +00:00 committed by Greg Kroah-Hartman
parent be535c9a05
commit 799a66ba36
1 changed files with 12 additions and 7 deletions
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19
drivers/staging/comedi/kcomedilib/kcomedilib_main.c
View File

@ -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;
return dev;
if (retval == NULL)
comedi_dev_put(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;
}