drm/dp_mst: Handle torn-down topology gracefully in drm_dp_mst_topology_queue_probe()

Overview

In the Linux kernel, the following vulnerability has been resolved:

drm/dp_mst: Handle torn-down topology gracefully in drm_dp_mst_topology_queue_probe()

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.

Affected

• Linux >= 5f57a96e92c60f62da91d58ceb5e5acd40e7d594 < b1d05cc61dfa6c4bd5e67855bec6a03e955f512d
• Linux >= dbaeef363ea54f4c18112874b77503c72ba60fec < 4ed6d08c4a59ee6a8cb806347f6d9873de5d229e
• Linux >= dbaeef363ea54f4c18112874b77503c72ba60fec < 8c6d84a54823cd839e6ce22af559925f1320c310
• Linux >= dbaeef363ea54f4c18112874b77503c72ba60fec < afdff9103818656627920c21822e48a6dae2906f
• Linux >= dbaeef363ea54f4c18112874b77503c72ba60fec < 613059875958e7b217b250ed14c3b189f9488421
• Linux >= 6.6.86 < 6.6.148
• Linux 6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.