[PATCH 1/5] 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>



drivers/base/driver.c | 7 +++++--
drivers/input/gameport/gameport.c | 1 -
drivers/input/serio/serio.c | 1 -
drivers/media/video/cx18/cx18-alsa-main.c | 1 -
drivers/media/video/ivtv/ivtvfb.c | 2 --
drivers/media/video/s5p-fimc/fimc-mdevice.c | 5 +-
drivers/media/video/s5p-tv/mixer_video.c | 1 -
drivers/s390/net/smsgiucv_app.c | 9 ++++--
8 files changed, 10 insertions(+), 17 deletions(-)

Index: usb-3.3/drivers/base/driver.c
usb-3.3.orig/drivers/base/driver.c
+++ usb-3.3/drivers/base/driver.c
@@ -234,7 +234,6 @@ int driver_register(struct device_driver

other = driver_find(drv->name, drv->bus);
if (other) {
- put_driver(other);
printk(KERN_ERR "Error: Driver '%s' is already registered, "
"aborting...", drv->name);
return -EBUSY;
@@ -275,7 +274,9 @@ EXPORT_SYMBOL_GPL(driver_unregister);
* 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 device_driver *driver_find(const
struct driver_private *priv;

if (k) {
+ /* Drop reference added by kset_find_obj() */
+ kobject_put(k);
priv = to_driver(k);
return priv->driver;
}
Index: usb-3.3/drivers/input/gameport/gameport.c
usb-3.3.orig/drivers/input/gameport/gameport.c
+++ usb-3.3/drivers/input/gameport/gameport.c
@@ -449,7 +449,6 @@ static ssize_t gameport_rebind_driver(st
} else if ((drv = driver_find(buf, &gameport_bus)) != NULL) {
gameport_disconnect_port(gameport);
error = gameport_bind_driver(gameport, to_gameport_driver(drv));
- put_driver(drv);
} else {
error = -EINVAL;
}
Index: usb-3.3/drivers/input/serio/serio.c
usb-3.3.orig/drivers/input/serio/serio.c
+++ usb-3.3/drivers/input/serio/serio.c
@@ -441,7 +441,6 @@ static ssize_t serio_rebind_driver(struc
} else if ((drv = driver_find(buf, &serio_bus)) != NULL) {
serio_disconnect_port(serio);
error = serio_bind_driver(serio, to_serio_driver(drv));
- put_driver(drv);
serio_remove_duplicate_events(serio, SERIO_RESCAN_PORT);
} else {
error = -EINVAL;
Index: usb-3.3/drivers/media/video/cx18/cx18-alsa-main.c
usb-3.3.orig/drivers/media/video/cx18/cx18-alsa-main.c
+++ usb-3.3/drivers/media/video/cx18/cx18-alsa-main.c
@@ -285,7 +285,6 @@ static void __exit cx18_alsa_exit(void)

drv = driver_find("cx18", &pci_bus_type);
ret = driver_for_each_device(drv, NULL, NULL, cx18_alsa_exit_callback);
- put_driver(drv);

cx18_ext_init = NULL;
printk(KERN_INFO "cx18-alsa: module unload complete");
Index: usb-3.3/drivers/media/video/ivtv/ivtvfb.c
usb-3.3.orig/drivers/media/video/ivtv/ivtvfb.c
+++ usb-3.3/drivers/media/video/ivtv/ivtvfb.c
@@ -1293,7 +1293,6 @@ static int __init ivtvfb_init(void)

drv = driver_find("ivtv", &pci_bus_type);
err = driver_for_each_device(drv, NULL, &registered, ivtvfb_callback_init);
- put_driver(drv);
if (!registered) {
printk(KERN_ERR "ivtvfb: no cards found");
return -ENODEV;
@@ -1310,7 +1309,6 @@ static void ivtvfb_cleanup(void)

drv = driver_find("ivtv", &pci_bus_type);
err = driver_for_each_device(drv, NULL, NULL, ivtvfb_callback_cleanup);
- put_driver(drv);
}

module_init(ivtvfb_init);
Index: usb-3.3/drivers/media/video/s5p-fimc/fimc-mdevice.c
usb-3.3.orig/drivers/media/video/s5p-fimc/fimc-mdevice.c
+++ usb-3.3/drivers/media/video/s5p-fimc/fimc-mdevice.c
@@ -344,16 +344,13 @@ static int fimc_md_register_platform_ent
return -ENODEV;
ret = driver_for_each_device(driver, NULL, fmd,
fimc_register_callback);
- put_driver(driver);
if (ret)
return ret;

driver = driver_find(CSIS_DRIVER_NAME, &platform_bus_type);
- if (driver) {
+ if (driver)
ret = driver_for_each_device(driver, NULL, fmd,
csis_register_callback);
- put_driver(driver);
- }
return ret;
}

Index: usb-3.3/drivers/media/video/s5p-tv/mixer_video.c
usb-3.3.orig/drivers/media/video/s5p-tv/mixer_video.c
+++ usb-3.3/drivers/media/video/s5p-tv/mixer_video.c
@@ -58,7 +58,6 @@ static struct v4l2_subdev *find_and_regi
}

done:
- put_driver(drv);
return sd;
}

Index: usb-3.3/drivers/s390/net/smsgiucv_app.c
usb-3.3.orig/drivers/s390/net/smsgiucv_app.c
+++ usb-3.3/drivers/s390/net/smsgiucv_app.c
@@ -168,7 +168,7 @@ static int __init smsgiucv_app_init(void
rc = dev_set_name(smsg_app_dev, KMSG_COMPONENT);
if (rc) {
kfree(smsg_app_dev);
- goto fail_put_driver;
+ goto fail;
}
smsg_app_dev->bus = &iucv_bus;
smsg_app_dev->parent = iucv_root;
@@ -177,7 +177,7 @@ static int __init smsgiucv_app_init(void
rc = device_register(smsg_app_dev);
if (rc) {
put_device(smsg_app_dev);
- goto fail_put_driver;
+ goto fail;
}

/* convert sender to uppercase characters */
@@ -191,12 +191,11 @@ static int __init smsgiucv_app_init(void
rc = smsg_register_callback(SMSG_PREFIX, smsg_app_callback);
if (rc) {
device_unregister(smsg_app_dev);
- goto fail_put_driver;
+ goto fail;
}

rc = 0;
-fail_put_driver:
- put_driver(smsgiucv_drv);
+fail:
return rc;
}
module_init(smsgiucv_app_init);

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