Re: [Qemu-devel] [PATCH 06/21] qapi: dealloc visitor, fix premature free and iteration logic

[Anthony Liguori <aliguori@us.ibm.com>]

On 09/28/2011 09:44 AM, Luiz Capitulino wrote:
> From: Michael Roth<mdroth@linux.vnet.ibm.com>
>
> Currently we do 3 things wrong:
>
> 1) The list iterator, in practice, is used in a manner where the pointer
> we pass in is the same as the pointer we assign the output to from
> visit_next_list(). This causes an infinite loop where we keep freeing
> the same structures.
>
> 2) We attempt to free list->value rather than list. visit_type_<type>
> handles this. We should only be concerned with the containing list.
>
> 3) We free prematurely: iterator function will continue accessing values
> we've already freed.
>
> This patch should fix all of these issues. QmpOutputVisitor also suffers
> from 1).
>
> Signed-off-by: Michael Roth<mdroth@linux.vnet.ibm.com>
> Signed-off-by: Luiz Capitulino<lcapitulino@redhat.com>

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>

Regards,

Anthony Liguori

> ---
>   qapi/qapi-dealloc-visitor.c |   20 +++++++++++++++-----
>   1 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c
> index f629061..6b586ad 100644
> --- a/qapi/qapi-dealloc-visitor.c
> +++ b/qapi/qapi-dealloc-visitor.c
> @@ -26,6 +26,7 @@ struct QapiDeallocVisitor
>   {
>       Visitor visitor;
>       QTAILQ_HEAD(, StackEntry) stack;
> +    bool is_list_head;
>   };
>
>   static QapiDeallocVisitor *to_qov(Visitor *v)
> @@ -70,15 +71,24 @@ static void qapi_dealloc_end_struct(Visitor *v, Error **errp)
>
>   static void qapi_dealloc_start_list(Visitor *v, const char *name, Error **errp)
>   {
> +    QapiDeallocVisitor *qov = to_qov(v);
> +    qov->is_list_head = true;
>   }
>
> -static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList **list,
> +static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList **listp,
>                                              Error **errp)
>   {
> -    GenericList *retval = *list;
> -    g_free(retval->value);
> -    *list = retval->next;
> -    return retval;
> +    GenericList *list = *listp;
> +    QapiDeallocVisitor *qov = to_qov(v);
> +
> +    if (!qov->is_list_head) {
> +        *listp = list->next;
> +        g_free(list);
> +        return *listp;
> +    }
> +
> +    qov->is_list_head = false;
> +    return list;
>   }
>
>   static void qapi_dealloc_end_list(Visitor *v, Error **errp)