s390/cio: fix race condition during online processing

In the Linux kernel, the following vulnerability has been resolved:

s390/cio: fix race condition during online processing

A race condition exists in ccw_device_set_online() that can cause the online process to fail, leaving the affected device in an inconsistent state. As a result, subsequent attempts to set that device online fail with return code ENODEV.

The problem occurs when a path verification request arrives after a wait for final device state completed, but before the result state is evaluated.

Fix this by ensuring that the CCW-device lock is held between determining final state and checking result state.

Note that since:

commit 2297791c92d0 ("s390/cio: dont unregister subchannel from child-drivers")

path verification requests are much more likely to occur during boot, resulting in an increased chance of this race condition occurring.