Re: [PATCH v4 1/8] scsi: ufs: Flush exception event before suspend

[Can Guo]

On 2020-01-26 11:29, Bart Van Assche wrote:
> On 2020-01-22 23:25, Can Guo wrote:
> > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > index 1201578..c2de29f 100644
> > --- a/drivers/scsi/ufs/ufshcd.c
> > +++ b/drivers/scsi/ufs/ufshcd.c
> > @@ -4760,8 +4760,15 @@ static void ufshcd_slave_destroy(struct 
> > scsi_device *sdev)
> >  			 * UFS device needs urgent BKOPs.
> >  			 */
> >  			if (!hba->pm_op_in_progress &&
> > -			    ufshcd_is_exception_event(lrbp->ucd_rsp_ptr))
> > -				schedule_work(&hba->eeh_work);
> > +			    ufshcd_is_exception_event(lrbp->ucd_rsp_ptr)) {
> > +				/*
> > +				 * Prevent suspend once eeh_work is scheduled
> > +				 * to avoid deadlock between ufshcd_suspend
> > +				 * and exception event handler.
> > +				 */
> > +				if (schedule_work(&hba->eeh_work))
> > +					pm_runtime_get_noresume(hba->dev);
> > +			}
>
> Please combine the two logical tests with "&&" instead of nesting two
> if-statements inside each other.
>
> >  			break;
> >  		case UPIU_TRANSACTION_REJECT_UPIU:
> >  			/* TODO: handle Reject UPIU Response */
> > @@ -5215,7 +5222,14 @@ static void 
> > ufshcd_exception_event_handler(struct work_struct *work)
> >
> >  out:
> >  	scsi_unblock_requests(hba->host);
> > -	pm_runtime_put_sync(hba->dev);
> > +	/*
> > +	 * pm_runtime_get_noresume is called while scheduling
> > +	 * eeh_work to avoid suspend racing with exception work.
> > +	 * Hence decrement usage counter using pm_runtime_put_noidle
> > +	 * to allow suspend on completion of exception event handler.
> > +	 */
> > +	pm_runtime_put_noidle(hba->dev);
> > +	pm_runtime_put(hba->dev);
> >  	return;
> >  }
> >
> > @@ -7901,6 +7915,7 @@ static int ufshcd_suspend(struct ufs_hba *hba, 
> > enum ufs_pm_op pm_op)
> >  			goto enable_gating;
> >  	}
> >
> > +	flush_work(&hba->eeh_work);
> >  	ret = ufshcd_link_state_transition(hba, req_link_state, 1);
> >  	if (ret)
> >  		goto set_dev_active;
>
> I think this patch introduces a new race condition, namely the 
> following:
> - ufshcd_slave_destroy() tests pm_op_in_progress and reads the value
>   zero from that variable.
> - ufshcd_suspend() sets hba->pm_op_in_progress to one.
> - ufshcd_slave_destroy() calls schedule_work().
>
> How about fixing this race condition by calling
> pm_runtime_get_noresume() before checking pm_op_in_progress and by
> reallowing resume if no work is scheduled?
>
> Thanks,
>
> Bart.

Hi Bart,

If you apply this patch, you will find the change is not in
ufshcd_slave_destroy(), but in ufshcd_transfer_rsp_status().
So the racing you mentioned above does not exist.

Thanks,

Can Guo.