Re: [PATCH v4] scsi: ufs: Cleanup completed request without interrupt notification

[Stanley Chu <stanley.chu@mediatek.com>]

Hi Can,

On Sat, 2020-08-01 at 07:17 +0800, Can Guo wrote:
> Hi Bart,
> 
> On 2020-08-01 00:51, Bart Van Assche wrote:
> > On 2020-07-31 01:00, Can Guo wrote:
> >> AFAIK, sychronization of scsi_done is not a problem here, because scsi
> >> layer
> >> use the atomic state, namely SCMD_STATE_COMPLETE, of a scsi cmd to 
> >> prevent
> >> the concurrency of abort and real completion of it.
> >> 
> >> Check func scsi_times_out(), hope it helps.
> >> 
> >> enum blk_eh_timer_return scsi_times_out(struct request *req)
> >> {
> >> ...
> >>         if (rtn == BLK_EH_DONE) {
> >>                 /*
> >>                  * Set the command to complete first in order to 
> >> prevent
> >> a real
> >>                  * completion from releasing the command while error
> >> handling
> >>                  * is using it. If the command was already completed,
> >> then the
> >>                  * lower level driver beat the timeout handler, and it
> >> is safe
> >>                  * to return without escalating error recovery.
> >>                  *
> >>                  * If timeout handling lost the race to a real
> >> completion, the
> >>                  * block layer may ignore that due to a fake timeout
> >> injection,
> >>                  * so return RESET_TIMER to allow error handling 
> >> another
> >> shot
> >>                  * at this command.
> >>                  */
> >>                 if (test_and_set_bit(SCMD_STATE_COMPLETE, 
> >> &scmd->state))
> >>                         return BLK_EH_RESET_TIMER;
> >>                 if (scsi_abort_command(scmd) != SUCCESS) {
> >>                         set_host_byte(scmd, DID_TIME_OUT);
> >>                         scsi_eh_scmd_add(scmd);
> >>                 }
> >>         }
> >> }
> > 
> > I am familiar with this mechanism. My concern is that both the regular
> > completion path and the abort handler must call scsi_dma_unmap() before
> > calling cmd->scsi_done(cmd). I don't see how
> > test_and_set_bit(SCMD_STATE_COMPLETE, &scmd->state) could prevent that
> > the regular completion path and the abort handler call scsi_dma_unmap()
> > concurrently since both calls happen before the SCMD_STATE_COMPLETE bit
> > is set?
> > 
> > Thanks,
> > 
> > Bart.
> 
> For scsi_dma_unmap() part, that is true - we should make it serialized 
> with
> any other completion paths. I've found it during my fault injection 
> test, so
> I've made a patch to fix it, but it only comes in my next error recovery
> enhancement patch series. Please check the attachment.
> 

Your patch looks good to me.

I have the same idea before but I found that calling scsi_done() (by
__ufshcd_transfer_req_compl()) in ufshcd_abort() in old kernel (e.g.,
4.14) will cause issues but it has been resolved by introduced
SCMD_STATE_COMPLETE flag in newer kernel. So your patch makes sense.

Would you mind sending out this draft patch as a formal patch together
with my patch to fix issues in ufshcd_abort()? Our patches are aimed to
fix cases that host/device reset eventually not being triggered by the
result of ufshcd_abort(), for example, command is aborted successfully
or command is not pending in device with its doorbell also cleared.

Thanks,
Stanley Chu

> Thanks,
> 
> Can Guo.
>