[PATCH] drm/dp/mst: make sure mst_primary mstb is valid in work function

[Dave Airlie]

From: Daniel Vetter <daniel.vet...@ffwll.ch>

This validates the mst_primary under the lock, and then calls
into the check and send function. This makes the code a lot
easier to understand the locking rules in.

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c 
b/drivers/gpu/drm/drm_dp_mst_topology.c
index a9c437e..8a3bfcd 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1204,7 +1204,7 @@ static void drm_dp_check_and_send_link_address(struct 
drm_dp_mst_topology_mgr *m
                                               struct drm_dp_mst_branch *mstb)
 {
        struct drm_dp_mst_port *port;
-
+       struct drm_dp_mst_branch *mstb_child;
        if (!mstb->link_address_sent) {
                drm_dp_send_link_address(mgr, mstb);
                mstb->link_address_sent = true;
@@ -1219,17 +1219,31 @@ static void drm_dp_check_and_send_link_address(struct 
drm_dp_mst_topology_mgr *m
                if (!port->available_pbn)
                        drm_dp_send_enum_path_resources(mgr, mstb, port);

-               if (port->mstb)
-                       drm_dp_check_and_send_link_address(mgr, port->mstb);
+               if (port->mstb) {
+                       mstb_child = drm_dp_get_validated_mstb_ref(mgr, 
port->mstb);
+                       if (mstb_child) {
+                               drm_dp_check_and_send_link_address(mgr, 
mstb_child);
+                               drm_dp_put_mst_branch_device(mstb_child);
+                       }
+               }
        }
 }

 static void drm_dp_mst_link_probe_work(struct work_struct *work)
 {
        struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct 
drm_dp_mst_topology_mgr, work);
+       struct drm_dp_mst_branch *mstb;

-       drm_dp_check_and_send_link_address(mgr, mgr->mst_primary);
-
+       mutex_lock(&mgr->lock);
+       mstb = mgr->mst_primary;
+       if (mstb) {
+               kref_get(&mstb->kref);
+       }
+       mutex_unlock(&mgr->lock);
+       if (mstb) {
+               drm_dp_check_and_send_link_address(mgr, mstb);
+               drm_dp_put_mst_branch_device(mstb);
+       }
 }

 static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
-- 
2.4.1