On Mon, Nov 10, 2014 at 7:41 AM, Dave Airlie <airlied@xxxxxxxxx> wrote:
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index ce1113c..f703a5b 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -882,8 +882,10 @@ static struct drm_dp_mst_branch *drm_dp_mst_get_validated_mstb_ref_locked(struct
> struct drm_dp_mst_port *port;
> struct drm_dp_mst_branch *rmstb;
> if (to_find == mstb) {
> - kref_get(&mstb->kref);
> - return mstb;
> + if (!kref_get_unless_zero(&mstb->kref))
> + return NULL;
> + else
> + return mstb;
> }
> list_for_each_entry(port, &mstb->ports, next) {
> if (port->mstb) {
kref_get_unless_zero only works with the lookup structure is protected
through some locking. But the list removal in
drm_dp_destroy_mst_branch_device is outside the mgr->glock, so that
needs to be moved I think. That's not directly required by
kref_get_unless_zero, just another effect of the ports list not
holding a full reference.
Aside for paranoia I'd put a mutex check next to the
kref_get_unles_zero, just to document which lock protects this weak
reference. And even more tangential: We should probably flatten the
recursion, or add a comment stating that the dp spec limits recursion
sufficiently.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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