[PATCH 3/9] driver core: warn should device_move try to move a need_parent_lock device

Currently, no device has need_parent_lock set and is moved by
device_move. need_parent_lock is only set by the usb bus and very
few device types ever use device_move.

Add a warning to device_move to catch should it ever be used on a
device with need_parent_lock set. The combination would break
the immutable relationship needed between parent and child for
need_parent_lock when locking and unlocking both.

Signed-off-by: David Jeffery <[email protected]>
Tested-by: Laurence Oberman <[email protected]>
---
 drivers/base/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index bd9c2921e326..75f5931165a8 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4712,6 +4712,14 @@ int device_move(struct device *dev, struct device *new_parent,
 	if (!dev)
 		return -EINVAL;
 
+	/*
+	 * device_move() should not be used on devices with need_parent_lock
+	 * set. Concurrent reparenting will violate the immutable
+	 * relationship needed while locking and unlocking both parent and
+	 * child.
+	 */
+	WARN_ON(dev->bus && dev->bus->need_parent_lock);
+
 	device_pm_lock();
 	new_parent = get_device(new_parent);
 	new_parent_kobj = get_device_parent(dev, new_parent);
-- 
2.55.0