Re: [Xen-devel] [PATCH] libxl: do not fail device removal if backend domain is gone

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Feb 09, 2018 at 12:22:13AM +0100, Marek Marczykowski-Górecki wrote:
> Backend domain may be independently destroyed - there is no
> synchronization of libxl structures (including /libxl tree) elsewhere.
> Backend might also remove the device info from its backend xenstore
> subtree on its own.
> If such situation is detected, do not fail the removal, but finish the
> cleanup of the frontend side.
> 
> This is just workaround, the real fix should watch when the device
> backend is removed (including backend domain destruction) and remove
> frontend at that time. And report such event to higher layer code, so
> for example libvirt could synchronize its state.
> 
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> ---
>  tools/libxl/libxl_device.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
> index 1b796bd392..1f58a99a23 100644
> --- a/tools/libxl/libxl_device.c
> +++ b/tools/libxl/libxl_device.c
> @@ -997,6 +997,13 @@ void libxl__initiate_device_generic_remove(libxl__egc 
> *egc,
>              goto out;
>          }
>  
> +        /* if state_path is empty, assume backend is gone (backend domain
> +         * shutdown?), cleanup frontend only; rc=0 */
> +        if (!state) {
> +            LOG(WARN, "backend %s already removed, cleanup frontend only", 
> be_path);
> +            goto out;
> +        }
> +

I think INFO should be used instead of WARN, since this doesn't look
to be a cause for concern from an admin PoV.

I'm also wondering, if you jump to 'out' here, you avoid the call to
libxl__xs_transaction_commit and instead end up calling
libxl__xs_transaction_abort, which means the above call to
libxl__xs_path_cleanup will not be committed to xenstore, is this
really desired?

It seems to me libxl might leak xenstore frontend entries in that
case.

Thanks, Roger.

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