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

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

Hi Can,

On Mon, 2020-08-03 at 13:14 +0800, Can Guo wrote:
> Hi Stanley,
> 
> On 2020-08-03 11:00, Stanley Chu wrote:
> > 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
> > 
> 
> I don't quite actually follow your fix here and I didn't test the 
> similar
> fault injection scenario like you do here, so I am not sure if I should
> just absorb your fix into mine. How about I put my fix in my current 
> error
> recovery patch series (maybe in next version of it) and you can give 
> your
> review. So you can still go with your fix as it is. Mine will be picked 
> up
> later by Martin. What do you think?
> 

Sure, that's good to me.

Thanks,

Stanley Chu

> Thanks,
> 
> Can Guo.
> 
> >> Thanks,
> >> 
> >> Can Guo.
> >> 

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