[PATCH 0/1][H] Fix disk hot removal regression in s390x under kvm

[Seth Forshee]

BugLink: https://bugs.launchpad.net/bugs/1925211

[Impact]

Hot removal of disks under kvm on s390 does not result in the kernel
removing the block device, which can lead to hung tasks and other
issues.

[Fix]

A bisect identified commit 8cc0dcfdc1c0 "s390/cio: remove pm support
from ccw bus driver" as introducing the regression. Reverting this patch
fixed the problem in testing.

[Test Plan]

See steps to reproduce the bug in the original description below. To
test, execute these steps and confirm that the block device gets removed
as expected.

[Where problems could occur]

The fix is a revert of the changes which introduced this regression. The
original commit was a removal of supposedly unused code, but it seems a
mistake was made in the logic around unregistering of disks. Reverting
the changes could have potential to introduce bugs related to other virt
devices, especially if it interacts badly with subsequent driver
changes. However, the patch reverted cleanly, and reverting restores the
code to the state which has been working well in previous kernels and
seems like the lowest risk option until a proper fix is available
upstream.

---

Seth Forshee (1):
  UBUNTU: SAUCE: Revert "s390/cio: remove pm support from ccw bus
    driver"

 arch/s390/include/asm/ccwdev.h |  10 ++
 drivers/s390/cio/cmf.c         |   5 +
 drivers/s390/cio/device.c      | 247 ++++++++++++++++++++++++++++++++-
 drivers/s390/cio/device.h      |   1 +
 drivers/s390/cio/device_fsm.c  |   6 +
 drivers/s390/cio/io_sch.h      |   1 +
 6 files changed, 268 insertions(+), 2 deletions(-)