Re: [PATCH 3/3] iotests/283: Check that finalize drops backup-top

[Max Reitz <mreitz@redhat.com>]

On 19.02.21 16:33, Max Reitz wrote:
> Without any of HEAD^ or HEAD^^ applied, qemu will most likely crash on
> the qemu-io invocation, for a variety of immediate reasons.  The
> underlying problem is generally a use-after-free access into
> backup-top's BlockCopyState.
> 
> With only HEAD^ applied, qemu-io will run into an EIO (which is not
> capture by the output, but you can see that the qemu-io invocation will
> be accepted (i.e., qemu-io will run) in contrast to the reference
> output, where the node name cannot be found), and qemu will then crash
> in query-named-block-nodes: bdrv_get_allocated_file_size() detects
> backup-top to be a filter and passes the request through to its child.
> However, after bdrv_backup_top_drop(), that child is NULL, so the
> recursive call crashes.
> 
> With HEAD^^ applied, this test should pass.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>   tests/qemu-iotests/283     | 55 ++++++++++++++++++++++++++++++++++++++
>   tests/qemu-iotests/283.out | 15 +++++++++++
>   2 files changed, 70 insertions(+)
> 
> diff --git a/tests/qemu-iotests/283 b/tests/qemu-iotests/283
> index 79643e375b..509dcbbcf4 100755
> --- a/tests/qemu-iotests/283
> +++ b/tests/qemu-iotests/283
> @@ -97,3 +97,58 @@ vm.qmp_log('blockdev-add', **{
>   vm.qmp_log('blockdev-backup', sync='full', device='source', target='target')
>   
>   vm.shutdown()
> +
> +
> +"""
> +Check that the backup-top node is gone after job-finalize.
> +
> +During finalization, the node becomes inactive and can no longer
> +function.  If it is still present, new parents might be attached, and
> +there would be no meaningful way to handle their I/O requests.
> +"""

Oh no, 297/pylint complains that this “string statement has no effect”. 
  Guess it should be a normal comment under the following print() then...

Max

> +print('\n=== backup-top should be gone after job-finalize ===\n')