RE: [RFC PATCH v3] scsi: ufs: Quiesce all scsi devices before shutdown

[Avri Altman]

> 
> Hi Bart,
> 
> On Sat, 2020-07-11 at 20:21 -0700, Bart Van Assche wrote:
> > On 2020-07-06 06:22, Stanley Chu wrote:
> > > +static void ufshcd_cleanup_queue(struct scsi_device *sdev, void *data)
> > > +{
> > > +   if (sdev->request_queue)
> > > +           blk_cleanup_queue(sdev->request_queue);
> > > +}
> >
> > No SCSI LLD should ever call blk_cleanup_queue() directly for
> > sdev->request_queue. Only the SCSI core should call blk_cleanup_queue()
> > directly for that queue.
> 
> Got it.
> 
> So may I focus on fixing racing first by quiecsing all SCSI devices only
> and do not touch blk_cleanup_queue() in UFS driver, just like v2?
> 
> 
> > >  int ufshcd_shutdown(struct ufs_hba *hba)
> > >  {
> > >     int ret = 0;
> > > +   struct scsi_target *starget;
> > >
> > >     if (!hba->is_powered)
> > >             goto out;
> > > @@ -8612,7 +8632,25 @@ int ufshcd_shutdown(struct ufs_hba *hba)
> > >                     goto out;
> > >     }
> > >
> > > +   /*
> > > +    * Quiesce all SCSI devices to prevent any non-PM requests sending
> > > +    * from block layer during and after shutdown.
> > > +    *
> > > +    * Here we can not use blk_cleanup_queue() since PM requests
> > > +    * (with BLK_MQ_REQ_PREEMPT flag) are still required to be sent
> > > +    * through block layer. Therefore SCSI command queued after the
> > > +    * scsi_target_quiesce() call returned will block until
> > > +    * blk_cleanup_queue() is called.
> > > +    *
> > > +    * Besides, scsi_target_"un"quiesce (e.g., scsi_target_resume) can
> > > +    * be ignored since shutdown is one-way flow.
> > > +    */
> > > +   ufshcd_scsi_for_each_sdev(ufshcd_quiece_sdev);
> > > +
> > >     ret = ufshcd_suspend(hba, UFS_SHUTDOWN_PM);
> > > +
> > > +   /* Set queue as dying to not block queueing commands */
> > > +   ufshcd_scsi_for_each_sdev(ufshcd_cleanup_queue);
> > >  out:
> > >     if (ret)
> > >             dev_err(hba->dev, "%s failed, err %d\n", __func__, ret);
> > >
> >
> > What is the purpose of ufshcd_shutdown()? Why does this function exist?
> > How about removing the calls to ufshcd_shutdown() and invoking power
> down
> > code from inside sd_suspend_common() instead?
> 
> ufshcd_shutdown() configures below things different from or more than
> what sd_suspend_common() can do now,
> 
> - Set link as OFF state
> - Regulator and clock toggling according to required low-power state for
> shutdown
> - Auto BKOP toggling
> - Vendor-specific shutdown flow ...etc.
> 
> Therefore UFS shutdown callback would be still required.
And this is also why, that each chipset vendor implement its own dev_pm_ops.

Thanks,
Avri

> 
> Thanks,
> Stanley Chu