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Re: [Xen-devel] [Qemu-block] [PATCH] xen-block: treat XenbusStateUnknown the same as XenbusStateClosed
- To: Paul Durrant <paul.durrant@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, qemu-devel@xxxxxxxxxx, qemu-block@xxxxxxxxxx
- From: John Snow <jsnow@xxxxxxxxxx>
- Date: Fri, 20 Sep 2019 17:10:54 -0400
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- Cc: Kevin Wolf <kwolf@xxxxxxxxxx>, Anthony Perard <anthony.perard@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Mark Syms <mark.syms@xxxxxxxxxx>, Max Reitz <mreitz@xxxxxxxxxx>
- Delivery-date: Fri, 20 Sep 2019 21:11:13 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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 <mark.syms@xxxxxxxxxx>
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
> Cc: Kevin Wolf <kwolf@xxxxxxxxxx>
> Cc: Max Reitz <mreitz@xxxxxxxxxx>
> ---
> 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);
>
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