Re: [RFC PATCH v1 18/25] hw/xen: Avoid crash when backend watch fires too early

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 02/03/2023 15:34, David Woodhouse wrote:
> From: Paul Durrant <pdurrant@xxxxxxxxxx>
>
> The xen-block code ends up calling aio_poll() through blkconf_geometry(),
> which means we see watch events during the indirect call to
> xendev_class->realize() in xen_device_realize(). Unfortunately this call
> is made before populating the initial frontend and backend device nodes
> in xenstore and hence xen_block_frontend_changed() (which is called from
> a watch event) fails to read the frontend's 'state' node, and hence
> believes the device is being torn down. This in-turn sets the backend
> state to XenbusStateClosed and causes the device to be deleted before it
> is fully set up, leading to the crash.
> By simply moving the call to xendev_class->realize() after the initial
> xenstore nodes are populated, this sorry state of affairs is avoided.
>
> Reported-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> ---
>   hw/xen/xen-bus.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
Reviewed-by: Paul Durrant <paul@xxxxxxx>