Re: [Qemu-block] [PATCH] xen-block: treat XenbusStateUnknown the same as XenbusStateClosed

[John Snow]

On 9/18/19 7:57 AM, Paul Durrant wrote:
> When a frontend gracefully disconnects from an offline backend, it will
> set its own state to XenbusStateClosed. The code in xen-block.c correctly
> deals with this and sets the backend into XenbusStateClosed. Unfortunately
> it is possible for toolstack to actually delete the frontend area
> before the state key has been read, leading to an apparent frontend state
> of XenbusStateUnknown. This prevents the backend state from transitioning
> to XenbusStateClosed and hence leaves it limbo.
> 

Does the 0 come from a read into de-allocated memory?

--js

> This patch simply treats a frontend state of XenbusStateUnknown the same
> as XenbusStateClosed, which will unblock the backend in these circumstances.
> 
> Reported-by: Mark Syms <address@hidden>
> Signed-off-by: Paul Durrant <address@hidden>
> ---
> Cc: Stefano Stabellini <address@hidden>
> Cc: Anthony Perard <address@hidden>
> Cc: Kevin Wolf <address@hidden>
> Cc: Max Reitz <address@hidden>
> ---
>  hw/block/xen-block.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
> index f77343db60..879fc310a4 100644
> --- a/hw/block/xen-block.c
> +++ b/hw/block/xen-block.c
> @@ -313,6 +313,7 @@ static void xen_block_frontend_changed(XenDevice *xendev,
>          break;
>  
>      case XenbusStateClosed:
> +    case XenbusStateUnknown:
>          xen_block_disconnect(xendev, &local_err);
>          if (local_err) {
>              error_propagate(errp, local_err);
>