From db210da268ec537f8944ea5bc490184a6707c8a2 Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Thu, 4 Apr 2013 14:59:18 +0100 Subject: [PATCH] staging: comedi: add comedi_clear_board_dev() 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 Reviewed-by: H Hartley Sweeten Signed-off-by: Greg Kroah-Hartman --- 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 b5e4bf1373e2..dec04b9b025e 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; -- 2.39.5