On Tue, Aug 15, 2017 at 12:04:53PM +0800, Fam Zheng wrote:
> @@ -147,6 +166,24 @@ static void blk_root_activate(BdrvChild *child, Error **errp)
>  
>      blk->disable_perm = false;
>  
> +    blk_set_perm(blk, blk->perm, BLK_PERM_ALL, &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
> +        blk->disable_perm = true;
> +        return;
> +    }
> +
> +    if (runstate_check(RUN_STATE_INMIGRATE)) {
> +        /* Activation can happen when migration process is still active, for
> +         * example when nbd_server_add is called during non-shared storage
> +         * migration. Defer the shared_perm update to migration completion. */
> +        if (!blk->vmsh) {
> +            blk->vmsh = qemu_add_vm_change_state_handler(blk_vm_state_changed,
> +                                                         blk);

Please add a qemu_del_vm_change_state_handler() call to cover the case
where the BB is deleted before the migration state changes.

This is necessary to prevent a memory leak and a crash when the change
state handler is invoked.

Stefan