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Commit 9b28500a authored by Andy Walls's avatar Andy Walls Committed by Mauro Carvalho Chehab
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[media] lirc_zilog: Remove broken, ineffective reference counting 



The set_use_inc() and set_use_dec() functions tried to lock
the underlying bridge driver device instance in memory by
changing the use count on the device's i2c_clients.  This
worked for PCI devices (ivtv, cx18, bttv).  It doesn't
work for hot-pluggable usb devices (pvrusb2 and hdpvr).
With usb device instances, the driver may get locked into
memory, but the unplugged hardware is gone.

The set_use_inc() set_use_dec() functions also tried to have
lirc_zilog change its own module refernce count, which is
racy and not guaranteed to work.  The lirc_dev module does
actually perform proper module ref count manipulation on the
lirc_zilog module, so there is need for lirc_zilog to
attempt a buggy module get on itself anyway.

lirc_zilog also errantly called these functions on itself
in open() and close(), but lirc_dev did that already too.

So let's just gut the bodies of the set_use_*() functions,
and remove the extra calls to them from within lirc_zilog.

Proper reference counting of the struct IR, IR_rx, and IR_tx
objects -- to handle the case when the underlying
bttv, ivtv, cx18, hdpvr, or pvrusb2 bridge driver module or
device instance goes away -- will be added in subsequent
patches.

Signed-off-by: default avatarAndy Walls <awalls@md.metrocast.net>
Signed-off-by: default avatarJarod Wilson <jarod@redhat.com>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
parent 12d896e1

drivers/staging/lirc/lirc_zilog.c

+1 −31
Original line number Diff line number Diff line
@@ -305,34 +305,12 @@ static int lirc_thread(void *arg) 


static int set_use_inc(void *data)

{

	struct IR *ir = data;



	if (ir->l.owner == NULL || try_module_get(ir->l.owner) == 0)

		return -ENODEV;



	/* lock bttv in memory while /dev/lirc is in use  */

	/*

	 * this is completely broken code. lirc_unregister_driver()

	 * must be possible even when the device is open

	 */

	if (ir->rx != NULL)

		i2c_use_client(ir->rx->c);

	if (ir->tx != NULL)

		i2c_use_client(ir->tx->c);



	return 0;

}



static void set_use_dec(void *data)

{

	struct IR *ir = data;



	if (ir->rx)

		i2c_release_client(ir->rx->c);

	if (ir->tx)

		i2c_release_client(ir->tx->c);

	if (ir->l.owner != NULL)

		module_put(ir->l.owner);

	return;

}



/* safe read of a uint32 (always network byte order) */
@@ -1098,7 +1076,6 @@ static struct IR *find_ir_device_by_minor(unsigned int minor) 
static int open(struct inode *node, struct file *filep)

{

	struct IR *ir;

	int ret;

	unsigned int minor = MINOR(node->i_rdev);



	/* find our IR struct */
@@ -1112,12 +1089,6 @@ static int open(struct inode *node, struct file *filep) 
	/* increment in use count */

	mutex_lock(&ir->ir_lock);

	++ir->open;

	ret = set_use_inc(ir);

	if (ret != 0) {

		--ir->open;

		mutex_unlock(&ir->ir_lock);

		return ret;

	}

	mutex_unlock(&ir->ir_lock);



	/* stash our IR struct */
@@ -1139,7 +1110,6 @@ static int close(struct inode *node, struct file *filep) 
	/* decrement in use count */

	mutex_lock(&ir->ir_lock);

	--ir->open;

	set_use_dec(ir);

	mutex_unlock(&ir->ir_lock);



	return 0;