Re: [Xen-devel] [PATCH 26/38] xen: xenbus: add missing put_device call

Ian Campbell
2014-01-06T11:10:04Z

On Mon, 2014-01-06 at 11:00 +0000, David Vrabel wrote:
> On 06/01/14 10:00, Ian Campbell wrote:
> > On Thu, 2014-01-02 at 13:53 +0000, David Vrabel wrote:
> >> On 19/12/13 15:03, Levente Kurusa wrote:
> >>> This is required so that we give up the last reference to the device.
> >>>
> >>> Signed-off-by: Levente Kurusa <levex@linux.com>
> >>> ---
> >>> drivers/xen/xenbus/xenbus_probe.c | 4 +++-
> >>> 1 file changed, 3 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
> >>> index 3c0a74b..4abb9ee 100644
> >>> --- a/drivers/xen/xenbus/xenbus_probe.c
> >>> +++ b/drivers/xen/xenbus/xenbus_probe.c
> >>> @@ -465,8 +465,10 @@ int xenbus_probe_node(struct xen_bus_type *bus,
> >>>
> >>> /* Register with generic device framework. */
> >>> err = device_register(&xendev->dev);
> >>> - if (err)
> >>> + if (err) {
> >>> + put_device(&xendev->dev);
> >>> goto fail;
> >>> + }
> >>>
> >>> return 0;
> >>> fail:
> >>
> >> There is a kfree(xendev) here so this introduces a double-free.
> >
> > How? put_device doesn't touch xendev itself, does it? It just drops the
> > ref on the dev member which is not separately dynamically allocated and
> > so not freed either.
>
> Releasing all references to the struct device frees the containing
> structure via xenbus->dev.release. i.e., xenbus_dev_release() which does
> kfree(xendev).

Ooh, twisty, well spotted ;-)

Ian.