drm/i915: Check that the vma hasn't been closed before we insert it

As there is a delay before we pin a vma, there is an opportunity for
another thread to have closed the vm and its vma (including us).
Check as soon as we acquire the vm->mutex and know the vm/vma is stable.

Closes: https://gitlab.freedesktop.org/drm/intel/issues/1291
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200221121940.2741563-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_vma.c

@@ -919,6 +919,11 @@ int i915_vma_pin(struct i915_vma *vma, u64 size, u64 alignment, u64 flags)
 	if (err)
 		goto err_fence;
 
+	if (unlikely(i915_vma_is_closed(vma))) {
+		err = -ENOENT;
+		goto err_unlock;
+	}
+
 	bound = atomic_read(&vma->flags);
 	if (unlikely(bound & I915_VMA_ERROR)) {
 		err = -ENOMEM;