A hotplug or link-loss event can tear down the MST topology
(setting mgr->mst_state = false and mgr->mst_primary = NULL) concurrently
with a caller invoking drm_dp_mst_topology_queue_probe(). Since the check
is already performed under mgr->lock, the condition is not a programming
error but a valid race -- the topology was valid when the caller decided
to call this function, but was torn down before the lock was acquired.
Replace the drm_WARN_ON() with a graceful early return. This eliminates
spurious kernel warnings and the resulting compositor crashes observed
when connecting/disconnecting DP MST monitors, while keeping the correct
behavior of doing nothing when MST is not active. A drm_dbg_mst() trace
is added so the skipped probe remains observable under MST debug logging.
The existing WARN_ON(mgr->mst_primary) in drm_dp_mst_topology_mgr_set_mst()
already catches the case where the topology is initialized twice, so no
diagnostic coverage is lost.
Fixes: dbaeef363ea5 ("drm/dp_mst: Add a helper to queue a topology probe")
Cc: Imre Deak <[email protected]>
Cc: Lyude Paul <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Jonas Emilsson <[email protected]>
---
drivers/gpu/drm/display/drm_dp_mst_topology.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c
b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 8757972e8..0cb341ce1 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -3738,8 +3738,10 @@ void drm_dp_mst_topology_queue_probe(struct
drm_dp_mst_topology_mgr *mgr)
{
mutex_lock(&mgr->lock);
- if (drm_WARN_ON(mgr->dev, !mgr->mst_state || !mgr->mst_primary))
+ if (!mgr->mst_state || !mgr->mst_primary) {
+ drm_dbg_mst(mgr->dev, "queue_probe skipped: topology torn
down\n");
goto out_unlock;
+ }
drm_dp_mst_topology_mgr_invalidate_mstb(mgr->mst_primary);
--
2.51.2
