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Sat, 02 May 2026 20:45:41 -0700 (PDT) Received: from jester ([159.192.33.28]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-364bdf54203sm10082989a91.7.2026.05.02.20.45.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 02 May 2026 20:45:40 -0700 (PDT) From: Jonas Emilsson To: dri-devel@lists.freedesktop.org Cc: Jonas Emilsson , Imre Deak , Lyude Paul , stable@vger.kernel.org, intel-gfx@lists.freedesktop.org Subject: [PATCH] drm/dp_mst: Handle torn-down topology gracefully in drm_dp_mst_topology_queue_probe() Date: Sun, 3 May 2026 05:45:33 +0200 Message-ID: <20260503034533.1023686-1-jonas.emilsson@gmail.com> X-Mailer: git-send-email 2.51.2 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 Cc: Lyude Paul Cc: stable@vger.kernel.org Cc: intel-gfx@lists.freedesktop.org Cc: dri-devel@lists.freedesktop.org Signed-off-by: Jonas Emilsson --- 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