[PATCH v6] drm/i915: Fix NULL pointer dereference in capture_engine

[Eugene Kobyak <eugene.kobyak@xxxxxxxxx>]

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

Fixes: e8a3319c31a1 ("drm/i915: Allow error capture without a request")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12309
Reviewed-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
Cc: John Harrison <John.C.Harrison@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v6.3+
Signed-off-by: Eugene Kobyak <eugene.kobyak@xxxxxxxxx>
---
v2:
  - return drm_info to separate condition
v3:
  - create separate condition which generate string if intel_context exist
v4:
  - rollback and add check intel_context in log condition
v5:
  - create separate string with guc_id if intel_context exist
v6:
  - print changed log if intel_context exist

 drivers/gpu/drm/i915/i915_gpu_error.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 135ded17334e..d88cefb889c3 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/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 gcu_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);
-- 
2.34.1