Add local function `comedi_clear_board_dev()` as a safer alternative to
`comedi_clear_board_minor()` when we already have a pointer to a `struct
comedi_device`. It uses the board minor device number stored in the
`struct comedi_device` (which must have already been initialized) and
only clears the entry in `comedi_board_minor_table[]` if it points to
the specified `struct comedi_device`. Rather than returning the old
table entry, it returns `true` if the entry matched (and so has just
been cleared) and returns `false` otherwise.
Call `comedi_clear_board_dev()` instead of `comedi_clear_board_minor()`
in `comedi_unlocked_ioctl()` (in the code that frees a dynamically
allocated comedi device detached by the `COMEDI_DEVCONFIG` ioctl). That
ought to return `true` but check it just in case before freeing the
device. There is still a race condition here which needs to be dealt
with once we've implemented reference counting for `struct
comedi_device`s.
Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
drivers/staging/comedi/comedi_fops.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index b5e4bf1..dec04b9 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -120,6 +120,20 @@ static void comedi_device_cleanup(struct comedi_device *dev)
mutex_destroy(&dev->mutex);
}
+static bool comedi_clear_board_dev(struct comedi_device *dev)
+{
+ unsigned int i = dev->minor;
+ bool cleared = false;
+
+ mutex_lock(&comedi_board_minor_table_lock);
+ if (dev == comedi_board_minor_table[i]) {
+ comedi_board_minor_table[i] = NULL;
+ cleared = true;
+ }
+ mutex_unlock(&comedi_board_minor_table_lock);
+ return cleared;
+}
+
static struct comedi_device *comedi_clear_board_minor(unsigned minor)
{
struct comedi_device *dev;
@@ -1766,9 +1780,7 @@ static long comedi_unlocked_ioctl(struct file *file, unsigned int cmd,
dev->minor >= comedi_num_legacy_minors) {
/* Successfully unconfigured a dynamically
* allocated device. Try and remove it. */
- struct comedi_device *devr;
- devr = comedi_clear_board_minor(dev->minor);
- if (dev == devr) {
+ if (comedi_clear_board_dev(dev)) {
mutex_unlock(&dev->mutex);
comedi_free_board_dev(dev);
return rc;
--
1.8.1.5
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