driver core: fix async device shutdown hang

Modify device_shutdown() so that supplier devices do not wait for
consumer devices to be shut down first when the devlink is sync state
only, since the consumer is not dependent on the supplier in this case.

Without this change, a circular dependency could hang the system.

Fixes: 8064952c ("driver core: shut down devices asynchronously")
Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20240919043143.1194950-1-stuart.w.hayes@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/core.c

@@ -4898,8 +4898,16 @@ void device_shutdown(void)
 
 		idx = device_links_read_lock();
 		list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,
-				device_links_read_lock_held())
+				device_links_read_lock_held()) {
+			/*
+			 * sync_state_only suppliers don't need to wait,
+			 * aren't reordered on devices_kset, so making them
+			 * wait could result in a hang
+			 */
+			if (device_link_flag_is_sync_state_only(link->flags))
+				continue;
 			link->supplier->p->shutdown_after = cookie;
+		}
 		device_links_read_unlock(idx);
 		put_device(dev);