Re: [PATCH v2 0/4] nbd/server: Quiesce coroutines on context switch

[Eric Blake <eblake@xxxxxxxxxx>]

On 12/14/20 11:05 AM, Sergio Lopez wrote:
> This series allows the NBD server to properly switch between AIO contexts,
> having quiesced recv_coroutine and send_coroutine before doing the transition.
> 
> We need this because we send back devices running in IO Thread owned contexts
> to the main context when stopping the data plane, something that can happen
> multiple times during the lifetime of a VM (usually during the boot sequence 
> or
> on a reboot), and we drag the NBD server of the correspoing export with it.
> 
> While there, fix also a problem caused by a cross-dependency between
> closing the export's client connections and draining the block
> layer. The visible effect of this problem was QEMU getting hung when
> the guest request a power off while there's an active NBD client.
> 
> v2:
>  - Replace "virtio-blk: Acquire context while switching them on
>  dataplane start" with "block: Honor blk_set_aio_context() context
>  requirements" (Kevin Wolf)
>  - Add "block: Avoid processing BDS twice in
>  bdrv_set_aio_context_ignore()"
>  - Add "block: Close block exports in two steps"
>  - Rename nbd_read_eof() to nbd_server_read_eof() (Eric Blake)
>  - Fix double space and typo in comment. (Eric Blake)

ping - where do we stand on this series?  Patches 1 and 3 have positive
reviews, I'll queue them now; patches 2 and 4 had enough comments that
I'm guessing I should wait for a v3?


> 
> Sergio Lopez (4):
>   block: Honor blk_set_aio_context() context requirements
>   block: Avoid processing BDS twice in bdrv_set_aio_context_ignore()
>   nbd/server: Quiesce coroutines on context switch
>   block: Close block exports in two steps
> 
>  block.c                         |  27 ++++++-
>  block/export/export.c           |  10 +--
>  blockdev-nbd.c                  |   2 +-
>  hw/block/dataplane/virtio-blk.c |   4 ++
>  hw/block/dataplane/xen-block.c  |   7 +-
>  hw/scsi/virtio-scsi.c           |   6 +-
>  include/block/export.h          |   4 +-
>  nbd/server.c                    | 120 ++++++++++++++++++++++++++++----
>  qemu-nbd.c                      |   2 +-
>  stubs/blk-exp-close-all.c       |   2 +-
>  10 files changed, 156 insertions(+), 28 deletions(-)
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org