CVE-2026-68429

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

drm/dpmst: Handle torn-down topology gracefully in drmdpmsttopologyqueueprobe()

A hotplug or link-loss event can tear down the MST topology (setting mgr->mststate = false and mgr->mstprimary = NULL) concurrently with a caller invoking drmdpmsttopologyqueue_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 drmWARNON() 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 drmdbgmst() trace is added so the skipped probe remains observable under MST debug logging.

The existing WARNON(mgr->mstprimary) in drmdpmsttopologymgrsetmst() already catches the case where the topology is initialized twice, so no diagnostic coverage is lost.