Fixes the following scenario:
1. Page table bo allocated in vram and linked to man->lru.
tbo->list_kref.refcount=2
2. Page table bo is swapped out and removed from man->lru.
tbo->list_kref.refcount=1
3. Command submission from userspace. Page table bo is moved
to vram. ttm_bo_move_to_lru_tail() link it to man->lru and
don't increase the kref count.
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Flora Cui <Flora.Cui@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
56fc350224