drm/i915: Do not access rq->engine without a reference

In i915_fence_get_driver_name(), user may not hold a
reference to rq->engine. Hence do not access it. Instead,
store required device private pointer in 'rq->i915' and use it.
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Suggested-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220614184348.23746-2-ramalingam.c@intel.com

drivers/gpu/drm/i915/i915_request.c

@@ -60,7 +60,7 @@ static struct kmem_cache *slab_execute_cbs;
 
 static const char *i915_fence_get_driver_name(struct dma_fence *fence)
 {
-	return dev_name(to_request(fence)->engine->i915->drm.dev);
+	return dev_name(to_request(fence)->i915->drm.dev);
 }
 
 static const char *i915_fence_get_timeline_name(struct dma_fence *fence)
@@ -937,6 +937,7 @@ __i915_request_create(struct intel_context *ce, gfp_t gfp)
 	rq->engine = ce->engine;
 	rq->ring = ce->ring;
 	rq->execution_mask = ce->engine->mask;
+	rq->i915 = ce->engine->i915;
 
 	ret = intel_timeline_get_seqno(tl, rq, &seqno);
 	if (ret)

drivers/gpu/drm/i915/i915_request.h

@@ -196,6 +196,8 @@ struct i915_request {
 	struct dma_fence fence;
 	spinlock_t lock;
 
+	struct drm_i915_private *i915;
+
 	/**
 	 * Context and ring buffer related to this request
 	 * Contexts are refcounted, so when this request is associated with a