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

[Bart Van Assche <bvanassche@acm.org>]

On 2020-02-02 22:23, Can Guo wrote:
> On 2020-01-26 11:29, Bart Van Assche wrote:
>> On 2020-01-22 23:25, Can Guo wrote:
>>>              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?
> 
> 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.

Hi Can,

Apparently I got a function name wrong. Can the following race condition
happen:
- ufshcd_transfer_rsp_status() tests pm_op_in_progress and reads the
  value zero from that variable.
- ufshcd_suspend() sets hba->pm_op_in_progress to one.
- ufshcd_suspend() calls flush_work(&hba->eeh_work).
- ufshcd_transfer_rsp_status() calls schedule_work(&hba->eeh_work).

Thanks,

Bart.