drm/i915: Serialise execbuf operation after a dma-buf reservation object

Now that we can wait upon fences before emitting the request, it becomes
trivial to wait upon any implicit fence provided by the dma-buf
reservation object.

To protect against failure, we force any asynchronous waits on a foreign
fence to timeout after 10s - so that a stall in another driver does not
permanently cripple ourselves. Still unpleasant though!

Testcase: igt/prime_vgem/fence-wait
Signed-off-by: Chris Wilson <[e-mail]>
Reviewed-by: John Harrison <[e-mail]>
Reviewed-by: Joonas Lahtinen <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/i915_gem_execbuffer.c

···
 
 	list_for_each_entry(vma, vmas, exec_list) {
 		struct drm_i915_gem_object *obj = vma->obj;
+		struct reservation_object *resv;
 
 		if (obj->flags & other_rings) {
 			ret = i915_gem_request_await_object
 				(req, obj, obj->base.pending_write_domain);
 			if (ret)
+				return ret;
+		}
+
+		resv = i915_gem_object_get_dmabuf_resv(obj);
+		if (resv) {
+			ret = i915_sw_fence_await_reservation
+				(&req->submit, resv, &i915_fence_ops,
+				 obj->base.pending_write_domain, 10*HZ,
+				 GFP_KERNEL | __GFP_NOWARN);
+			if (ret < 0)
 				return ret;
 		}