On Wed, 2018-09-19 at 10:21 +0800, jianchao.wang wrote:

On 09/19/2018 01:44 AM, Bart Van Assche wrote:

quoted

There is only one blk_pm_request_resume() call and that call is
inside blk_queue_enter() after the pm_only counter has been
checked.

For the legacy block layer, nr_pending is increased after the
blk_queue_enter() call from inside blk_old_get_request() succeeded.

So I don't see how blk_pm_request_resume() or q->nr_pending++ could
escape from the preempt checking?

For example:


blk_pre_runtime_suspend                    generic_make_request
                                             blk_queue_enter  //
success here, no blk_pm_request_resume here
                                             blk_mq_make_requset
blk_set_pm_only

if (blk_requests_in_flight(q) == 0) {
  synchronize_rcu();
  if (blk_requests_in_flight(q) == 0)
    ret = 0;
  }
                                             blk_mq_get_request

Hello Jianchao,

I think you are right. I will add a q_usage_counter check before
setting 'ret' to zero.

Bart.