drm/i915: Fix NULL pointer dereference in capture_engine

When the intel_context structure contains NULL,
it raises a NULL pointer dereference error in drm_info().

Fixes: e8a3319 ("drm/i915: Allow error capture without a request")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12309
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: <stable@vger.kernel.org> # v6.3+
Signed-off-by: Eugene Kobyak <eugene.kobyak@intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/xmsgfynkhycw3cf56akp4he2ffg44vuratocsysaowbsnhutzi@augnqbm777at
(cherry picked from commit 754302a)
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>

Author: eugene-kobyak

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -1643,9 +1643,21 @@ capture_engine(struct intel_engine_cs *engine,
 		return NULL;
 
 	intel_engine_get_hung_entity(engine, &ce, &rq);
-	if (rq && !i915_request_started(rq))
-		drm_info(&engine->gt->i915->drm, "Got hung context on %s with active request %lld:%lld [0x%04X] not yet started\n",
-			 engine->name, rq->fence.context, rq->fence.seqno, ce->guc_id.id);
+	if (rq && !i915_request_started(rq)) {
+		/*
+		 * We want to know also what is the guc_id of the context,
+		 * but if we don't have the context reference, then skip
+		 * printing it.
+		 */
+		if (ce)
+			drm_info(&engine->gt->i915->drm,
+				 "Got hung context on %s with active request %lld:%lld [0x%04X] not yet started\n",
+				 engine->name, rq->fence.context, rq->fence.seqno, ce->guc_id.id);
+		else
+			drm_info(&engine->gt->i915->drm,
+				 "Got hung context on %s with active request %lld:%lld not yet started\n",
+				 engine->name, rq->fence.context, rq->fence.seqno);
+	}
 
 	if (rq) {
 		capture = intel_engine_coredump_add_request(ee, rq, ATOMIC_MAYFAIL);