drm: fix mutex leak in drm_dp_get_mst_branch_device

In Linux 4.3-rc5, there is an error case in drm_dp_get_branch_device
that returns without releasing mgr->lock, resulting a spew of kernel
messages about a kernel work function possibly having leaked a mutex
and presumably more serious adverse consequences later.  This patch
changes the error to "goto out" to unlock the mutex before returning.

[airlied: grabbed from drm-next as it fixes something we've seen]

Signed-off-by: Adam J. Richter <adam_richter2004@yahoo.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 5bca390d9ae26022df1be85d008ee7107d8aa9b8..809959d56d7826364b540204a16190aaf270f9c4 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1194,17 +1194,18 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_
 
                list_for_each_entry(port, &mstb->ports, next) {
                        if (port->port_num == port_num) {
-                               if (!port->mstb) {
+                               mstb = port->mstb;
+                               if (!mstb) {
                                        DRM_ERROR("failed to lookup MSTB with lct %d, rad %02x\n", lct, rad[0]);
-                                       return NULL;
+                                       goto out;
                                }
 
-                               mstb = port->mstb;
                                break;
                        }
                }
        }
        kref_get(&mstb->kref);
+out:
        mutex_unlock(&mgr->lock);
        return mstb;
 }