Re: [PATCH 2/2] block: bdrv_reopen() with backing file in different AioContext

[Alberto Garcia]

On Thu 27 Feb 2020 07:18:04 PM CET, Kevin Wolf wrote:
>      /*
> -     * TODO: before removing the x- prefix from x-blockdev-reopen we
> -     * should move the new backing file into the right AioContext
> -     * instead of returning an error.
> +     * Check AioContext compatibility so that the bdrv_set_backing_hd() call 
> in
> +     * bdrv_reopen_commit() won't fail.
>       */
> -    if (new_backing_bs) {
> -        if (bdrv_get_aio_context(new_backing_bs) != 
> bdrv_get_aio_context(bs)) {
> -            error_setg(errp, "Cannot use a new backing file "
> -                       "with a different AioContext");
> -            return -EINVAL;
> -        }
> +    if (!bdrv_reopen_can_attach(bs->backing, bs, new_backing_bs, errp)) {
> +        return -EINVAL;
>      }

What happens here now if 'new_backing_bs' is NULL ?

It seems that you would be calling bdrv_can_set_aio_context(NULL, ...),
and it looks like that would crash.

Berto