Driver core: driver_find() drops reference before returning
As part of the removal of get_driver()/put_driver(), this patch
(as1510) changes driver_find(); it now drops the reference it acquires
before returning. The patch also adjusts all the callers of
driver_find() to remove the now unnecessary calls to put_driver().
In addition, the patch adds a warning to driver_find(): Callers must
make sure the driver they are searching for does not get unloaded
while they are using it. This has always been the case; driver_find()
has never prevented a driver from being unregistered or unloaded.
Hence the patch will not introduce any new bugs. The existing callers
all seem to be okay in this respect, however I don't understand the
video drivers well enough to be certain about them.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Dmitry Torokhov <dmitry.torokhov@gmail.com>
CC: Kyungmin Park <kyungmin.park@samsung.com>
CC: Andy Walls <awalls@md.metrocast.net>
CC: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/base/driver.c b/drivers/base/driver.c
index b631f7c..e979cad 100644
--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -234,7 +234,6 @@
other = driver_find(drv->name, drv->bus);
if (other) {
- put_driver(other);
printk(KERN_ERR "Error: Driver '%s' is already registered, "
"aborting...\n", drv->name);
return -EBUSY;
@@ -275,7 +274,9 @@
* Call kset_find_obj() to iterate over list of drivers on
* a bus to find driver by name. Return driver if found.
*
- * Note that kset_find_obj increments driver's reference count.
+ * This routine provides no locking to prevent the driver it returns
+ * from being unregistered or unloaded while the caller is using it.
+ * The caller is responsible for preventing this.
*/
struct device_driver *driver_find(const char *name, struct bus_type *bus)
{
@@ -283,6 +284,8 @@
struct driver_private *priv;
if (k) {
+ /* Drop reference added by kset_find_obj() */
+ kobject_put(k);
priv = to_driver(k);
return priv->driver;
}