drm/i915: Retire requests before creating a new one

More fallout from

commit c8725f3dc0
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon Mar 17 12:21:55 2014 +0000

    drm/i915: Do not call retire_requests from wait_for_rendering

is that we can completely fill all of memory using small objects, such
that we exhaust the filp space, and spend all of our time evicting
objects from the aperture. As such, we never fill the ring, and never
trigger the last resort flushing in

commit 1cf0ba1474
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon May 5 09:07:33 2014 +0100

    drm/i915: Flush request queue when waiting for ring space

and so all the requests are left active and the objects keep that last
active reference. Eventually the system comes to a halt as it runs out
of memory.

The impact is mainly limited to test cases as regular userspace will
trigger retirement by manually checking whether an object is active.

Testcase: igt/gem_lut_handle
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78724
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Guo Jinxian <jinxianx.guo@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -610,6 +610,8 @@ i915_gem_execbuffer_reserve(struct intel_ring_buffer *ring,
 	if (list_empty(vmas))
 		return 0;
 
+	i915_gem_retire_requests_ring(ring);
+
 	vm = list_first_entry(vmas, struct i915_vma, exec_list)->vm;
 
 	INIT_LIST_HEAD(&ordered_vmas);