[bug report] drm/i915/gvt: Rework shadow graphic memory management code

[Dan Carpenter]

Hello Changbin Du,

The patch ede9d0cfcb78: "drm/i915/gvt: Rework shadow graphic memory
management code" from Jan 30, 2018, leads to the following Smatch
static checker warning:

	drivers/gpu/drm/i915/gvt/scheduler.c:796 prepare_workload()
	warn: inconsistent refcounting 'workload->shadow_mm->pincount.counter':

drivers/gpu/drm/i915/gvt/gtt.c
  2043  int intel_vgpu_pin_mm(struct intel_vgpu_mm *mm)
  2044  {
  2045          int ret;
  2046  
  2047          atomic_inc(&mm->pincount);
                ^^^^^^^^^^^^^^^^^^^^^^^^^

  2048  
  2049          if (mm->type == INTEL_GVT_MM_PPGTT) {
  2050                  ret = shadow_ppgtt_mm(mm);
  2051                  if (ret)
  2052                          return ret;

decrement the pincount on error?

  2053  
  2054                  mutex_lock(&mm->vgpu->gvt->gtt.ppgtt_mm_lock);
  2055                  list_move_tail(&mm->ppgtt_mm.lru_list,
  2056                                 &mm->vgpu->gvt->gtt.ppgtt_mm_lru_list_head);
  2057                  mutex_unlock(&mm->vgpu->gvt->gtt.ppgtt_mm_lock);
  2058          }
  2059  
  2060          return 0;
  2061  }

regards,
dan carpenter