[PATCH 1/2] drm/dp: look up the mstb passed into work function (v2)

[Dave Airlie <airlied@gmail.com>]

From: Dave Airlie <airlied@redhat.com>

We should validate the passed in mstb under the lock
this should stop us getting an invalid mstb here.

(first attempt with cancelling work has lockdep issues).
Bugzilla: https://bugs.archlinux.org/task/45369

v2: update bugzilla, add some notes on why passing mst_primary
is okay.

Signed-off-by: Dave Airlie <airlied@redhat.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index fb65f5d..3c7e5cd 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1198,9 +1198,14 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_
 }
 
 static void drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
-					       struct drm_dp_mst_branch *mstb)
+					       struct drm_dp_mst_branch *mstb_in)
 {
 	struct drm_dp_mst_port *port;
+	struct drm_dp_mst_branch *mstb;
+
+	mstb = drm_dp_get_validated_mstb_ref(mgr, mstb_in);
+	if (!mstb)
+		return;
 
 	if (!mstb->link_address_sent) {
 		drm_dp_send_link_address(mgr, mstb);
@@ -1219,12 +1224,20 @@ static void drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *m
 		if (port->mstb)
 			drm_dp_check_and_send_link_address(mgr, port->mstb);
 	}
+	drm_dp_put_mst_branch_device(mstb);
 }
 
 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);
-
+	/*
+	 * Note this passes mgr->mst_primary without validation
+	 * it could be a) valid, b) NULL, c) some value between
+	 * since we haven't taken the lock,
+	 * however the validation sequence in check and send
+	 * will take the lock, and if the value isn't valid
+	 * it will fail appropriately.
+	 */
 	drm_dp_check_and_send_link_address(mgr, mgr->mst_primary);
 
 }
-- 
2.4.1

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