hw/block/nvme: drain namespaces on sq deletion

hw/block/nvme: drain namespaces on sq deletion

For most commands, when issuing an AIO, the BlockAIOCB is stored in the
NvmeRequest aiocb pointer when the AIO is issued. The main use of this
is cancelling AIOs when deleting submission queues (it is currently not
used for Abort).

However, some commands like Dataset Management Zone Management Send
(zone reset) may involve more than one AIO and here the AIOs are issued
without saving a reference to the BlockAIOCB. This is a problem since
nvme_del_sq() will attempt to cancel outstanding AIOs, potentially with
an invalid BlockAIOCB since the aiocb pointer is not NULL'ed when the
request structure is recycled.

Fix this by

  1. making sure the aiocb pointer is NULL'ed when requests are recycled
  2. only attempt to cancel the AIO if the aiocb is non-NULL
  3. if any AIOs could not be cancelled, drain all aio as a last resort.

Fixes: dc04d25e2f3f ("hw/block/nvme: add support for the format nvm command")
Fixes: c94973288cd9 ("hw/block/nvme: add broadcast nsid support flush command")
Fixes: e4e430b3d6ba ("hw/block/nvme: add simple copy command")
Fixes: 5f5dc4c6a942 ("hw/block/nvme: zero out zones on reset")
Fixes: 2605257a26b8 ("hw/block/nvme: add the dataset management command")
Cc: Gollu Appalanaidu <anaidu.gollu@samsung.com>
Cc: Minwoo Im <minwoo.im@samsung.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
Reviewed-by: Minwoo Im <minwoo.im.dev@gmail.com>