Re: [PATCH v19 2/3] scsi: ufs: L2P map management for HPB read

[Can Guo]

On 2021-02-08 16:53, Daejun Park wrote:

@@ -342,13 +1208,14 @@ void ufshpb_suspend(struct ufs_hba *hba)
>          struct scsi_device *sdev;
>
>          shost_for_each_device(sdev, hba->host) {
> -                hpb = sdev->hostdata;
> +                hpb = ufshpb_get_hpb_data(sdev);
>                  if (!hpb)
>                          continue;
>
>                  if (ufshpb_get_state(hpb) != HPB_PRESENT)
>                          continue;
>                  ufshpb_set_state(hpb, HPB_SUSPEND);
> +                ufshpb_cancel_jobs(hpb);

Here may have a dead lock problem - in the case of runtime suspend,
when ufshpb_suspend() is invoked, all of hba's children scsi devices
are in RPM_SUSPENDED state. When this line tries to cancel a running
map work, i.e. when ufshpb_get_map_req() calls below lines, it will
be stuck at blk_queue_enter().

req = blk_get_request(hpb->sdev_ufs_lu->request_queue,
                      REQ_OP_SCSI_IN, 0);

Please check block layer power management, and see also commit
d55d15a33
("scsi: block: Do not accept any requests while suspended").

I am agree with your comment.
How about add BLK_MQ_REQ_NOWAIT flag on blk_get_request() to avoid
hang?

That won't work - BLK_MQ_REQ_NOWAIT allows one to fast fail from
blk_mq_get_tag(),
but blk_queue_enter() comes before __blk_mq_alloc_request();

In blk_queue_enter(), BLK_MQ_REQ_NOWAIT flag can make error than wait rpm

resume. Please refer following code.

Oops, sorry, my memory needs to be refreshed on that part.

But will BLK_MQ_REQ_NOWAIT flag breaks your original purpose? When
runtime suspend is out of the picture, if traffic is heavy on the
request queue, map_work() will be stopped frequently once it is
not able to get a request from the queue - that shall pull down the
efficiency of one map_work(), that may hurt random performance...

Can Guo.

int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
{
        const bool pm = flags & BLK_MQ_REQ_PM;

        while (true) {
                bool success = false;

                rcu_read_lock();
                if (percpu_ref_tryget_live(&q->q_usage_counter)) {
                        /*
                         * The code that increments the pm_only counter is
                         * responsible for ensuring that that counter is
                         * globally visible before the queue is unfrozen.
                         */
                        if ((pm && queue_rpm_status(q) != RPM_SUSPENDED) ||
                            !blk_queue_pm_only(q)) {
                                success = true;
                        } else {
                                percpu_ref_put(&q->q_usage_counter);
                        }
                }
                rcu_read_unlock();

                if (success)
                        return 0;

                if (flags & BLK_MQ_REQ_NOWAIT)
                        return -EBUSY;  <-- out from the function.

Thanks,
Daejun