4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Adam Richter <adamricht...@gmail.com>

commit 30730c7f5943b3beace1e29f7f1476e05de3da14 upstream.

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_richter2...@yahoo.com>
Signed-off-by: Daniel Vetter <daniel.vet...@ffwll.ch>
Signed-off-by: Dave Airlie <airl...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/gpu/drm/drm_dp_mst_topology.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1193,17 +1193,18 @@ static struct drm_dp_mst_branch *drm_dp_
 
                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;
 }


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