[bug report] drm/amdgpu: optimize the gpu reset for XGMI setup V2

[Dan Carpenter]

Hello Evan Quan,

This is a semi-automatic email about new static checker warnings.

The patch 9e94d22c0085: "drm/amdgpu: optimize the gpu reset for XGMI
setup V2" from Apr 16, 2020, leads to the following Smatch complaint:

    drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:4199 amdgpu_device_gpu_recover()
    error: we previously assumed 'hive' could be null (see line 4196)

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
  4195		list_for_each_entry(tmp_adev, device_list_handle, gmc.xgmi.head) {
  4196			if (!amdgpu_device_lock_adev(tmp_adev, !hive)) {
                                                               ^^^^^
There are a ton of double negatives in this snippet.

Assume hive is NULL, then not NULL is true, so in amdgpu_device_lock_adev()
we try to take the lock, and lets assume that fails.  That's only path
which returns false.  In other words, we know that "hive" is NULL inside
this condition.

  4197				DRM_INFO("Bailing on TDR for s_job:%llx, as another already in progress",
  4198					  job ? job->base.id : -1);
  4199				mutex_unlock(&hive->hive_lock);
                                              ^^^^
NULL dereference.

  4200				return 0;
  4201			}

regards,
dan carpenter