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

[Guilherme Piccoli]

On Wed, Apr 21, 2021 at 9:44 AM Seth Forshee <seth.forshee at canonical.com> wrote:
>
> 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.
>

Thanks Seth, LGTM:
Acked-by: Guilherme G. Piccoli <gpiccoli at canonical.com>