driver core: Fix unbalanced device reference in drivers_probe

bus_find_device_by_name() acquires a device reference which is never
released. This results in an object leak, which on older kernels
results in failure to release all resources of PCI devices. libvirt
uses drivers_probe to re-attach devices to the host after assignment
and is therefore a common trigger for this leak.

Example:

# cd /sys/bus/pci/
# dmesg -C
# echo 1 > devices/0000\:01\:00.0/sriov_numvfs
# echo 0 > devices/0000\:01\:00.0/sriov_numvfs
# dmesg | grep 01:10
pci 0000:01:10.0: [8086:10ca] type 00 class 0x020000
kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_add_internal: parent: '0000:00:01.0', set: 'devices'
kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_uevent_env
kobject: '0000:01:10.0' (ffff8801d79cd0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_uevent_env
kobject: '0000:01:10.0' (ffff8801d79cd0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_uevent_env
kobject: '0000:01:10.0' (ffff8801d79cd0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_cleanup, parent (null)
kobject: '0000:01:10.0' (ffff8801d79cd0a8): calling ktype release
kobject: '0000:01:10.0': free name

[kobject freed as expected]

# dmesg -C
# echo 1 > devices/0000\:01\:00.0/sriov_numvfs
# echo 0000:01:10.0 > drivers_probe
# echo 0 > devices/0000\:01\:00.0/sriov_numvfs
# dmesg | grep 01:10
pci 0000:01:10.0: [8086:10ca] type 00 class 0x020000
kobject: '0000:01:10.0' (ffff8801d79ce0a8): kobject_add_internal: parent: '0000:00:01.0', set: 'devices'
kobject: '0000:01:10.0' (ffff8801d79ce0a8): kobject_uevent_env
kobject: '0000:01:10.0' (ffff8801d79ce0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
kobject: '0000:01:10.0' (ffff8801d79ce0a8): kobject_uevent_env
kobject: '0000:01:10.0' (ffff8801d79ce0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
kobject: '0000:01:10.0' (ffff8801d79ce0a8): kobject_uevent_env
kobject: '0000:01:10.0' (ffff8801d79ce0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'

[no free]

Signed-off-by: Alex Williamson <[e-mail]>
Cc: [e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/bus.c

···
 				   const char *buf, size_t count)
 {
 	struct device *dev;
+	int err = -EINVAL;
 
 	dev = bus_find_device_by_name(bus, NULL, buf);
 	if (!dev)
 		return -ENODEV;
-	if (bus_rescan_devices_helper(dev, NULL) != 0)
-		return -EINVAL;
-	return count;
+	if (bus_rescan_devices_helper(dev, NULL) == 0)
+		err = count;
+	put_device(dev);
+	return err;
 }
 
 static struct device *next_device(struct klist_iter *i)