[PATCH v5] drm/i915: Fix NULL pointer dereference in capture_engine

[Eugene Kobyak]

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
Cc: John Harrison <John.C.Harrison at Intel.com>
Cc: <stable at vger.kernel.org> # v6.3+
Signed-off-by: Eugene Kobyak <eugene.kobyak at intel.com>
---
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
 drivers/gpu/drm/i915/i915_gpu_error.c | 9 ++++++---
 1 file changed, 6 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..4ca6b9872a48 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -1643,9 +1643,12 @@ 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)) {
+	        char guc_id[11];
+		ce ? snprintf(guc_id, sizeof(guc_id), " [0x%04x] ", ce->guc_id.id) : snprintf(guc_id, sizeof(guc_id), " ");
+	        drm_info(&engine->gt->i915->drm, "Got hung context on %s with active request %lld:%lld%snot yet started\n",
+	                 engine->name, rq->fence.context, rq->fence.seqno, guc_id);
+	}
 
 	if (rq) {
 		capture = intel_engine_coredump_add_request(ee, rq, ATOMIC_MAYFAIL);
-- 
2.34.1