Comment 63 for bug 507148

Here is the calling sequence before it gets to that error. Looks like it really is not able to allocate any more memory in some cases.

radeon_bo_list_validate():
r = ttm_bo_validate(&bo->tbo, &bo->placement, true, false);

ttm_bo_validate():
ret = ttm_bo_move_buffer(bo, placement, interruptible, no_wait);

ttm_bo_move_buffer():
        spin_lock(&bo->lock);
        ret = ttm_bo_wait(bo, false, interruptible, no_wait);
        spin_unlock(&bo->lock);

ttm_bo_wait():
ret = driver->sync_obj_wait(sync_obj, sync_obj_arg, lazy, interruptible);
@sync_obj_wait: See ttm_fence_api.h not found.

since radeon driver is in use, and these functions are setup by
the driver. sync_obj_wait maps to radeon_sync_obj_wait.

radeon_sync_obj_wait():
return radeon_fence_wait((struct radeon_fence *)sync_obj, interruptible);

radeon_fence_wait(): returns a negative number when a lot of windows are open.