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From: Markus Armbruster <armbru@redhat.com>
References: <1549377087-205549-1-git-send-email-imammedo@redhat.com>
Date: Wed, 13 Feb 2019 14:30:55 +0100
In-Reply-To: <1549377087-205549-1-git-send-email-imammedo@redhat.com> (Igor
	Mammedov's message of "Tue, 5 Feb 2019 15:31:27 +0100")
Message-ID: <877ee36cj4.fsf@dusky.pond.sub.org>
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Subject: Re: [Qemu-devel] [PATCH] hostmem: fix crash when querying empty
 host-nodes property via QMP
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To: Igor Mammedov <imammedo@redhat.com>
Cc: qemu-devel@nongnu.org, ehabkost@redhat.com

Igor Mammedov <imammedo@redhat.com> writes:

> QEMU will crashes with
>  qapi/qobject-output-visitor.c:210: qobject_output_complete: Assertion `qov->root && ((&qov->stack)->slh_first == ((void *)0))' failed
> when trying to get value of empty hostmem.host-nodes property.
>
> Fix it by calling visitor even if host-nodes wasn't set
> before exiting from property getter to return empty list.

host-nodes or host_nodes?

If local variable host_nodes: that one's always set.  The case you fix
has it set to NULL.

> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>  backends/hostmem.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/backends/hostmem.c b/backends/hostmem.c
> index 0c8ef17..fe14be5 100644
> --- a/backends/hostmem.c
> +++ b/backends/hostmem.c
> @@ -86,7 +86,7 @@ host_memory_backend_get_host_nodes(Object *obj, Visitor *v, const char *name,
>  
>      value = find_first_bit(backend->host_nodes, MAX_NODES);
>      if (value == MAX_NODES) {
> -        return;
> +        goto ret;
>      }
>  
>      *node = g_malloc0(sizeof(**node));
> @@ -104,6 +104,7 @@ host_memory_backend_get_host_nodes(Object *obj, Visitor *v, const char *name,
>          node = &(*node)->next;
>      } while (true);
>  
> +ret:
>      visit_type_uint16List(v, name, &host_nodes, errp);
>  }

Yes, an empty list needs to be visited just like a non-empty list.

Patch looks good.