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From: Stanley Chu <stanley.chu@mediatek.com>
To: Can Guo <cang@codeaurora.org>
Cc: Bart Van Assche <bvanassche@acm.org>,
	Avri Altman <Avri.Altman@wdc.com>, <linux-scsi@vger.kernel.org>,
	<martin.petersen@oracle.com>, <alim.akhtar@samsung.com>,
	<jejb@linux.ibm.com>, <beanhuo@micron.com>,
	<asutoshd@codeaurora.org>, <matthias.bgg@gmail.com>,
	<linux-mediatek@lists.infradead.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>, <kuohong.wang@mediatek.com>,
	<peter.wang@mediatek.com>, <chun-hung.wu@mediatek.com>,
	<andy.teng@mediatek.com>, <chaotian.jing@mediatek.com>,
	<cc.chou@mediatek.com>
Subject: Re: [PATCH v4] scsi: ufs: Cleanup completed request without interrupt notification
Date: Mon, 3 Aug 2020 11:00:55 +0800
Message-ID: <1596423655.32283.7.camel@mtkswgap22> (raw)
In-Reply-To: <548b602daa1e15415625cb8d1f81a208@codeaurora.org>

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.
> 


  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24 14:02 Stanley Chu
2020-07-27 11:18 ` Avri Altman
2020-07-31  1:30   ` Stanley Chu
2020-07-31  4:06     ` Bart Van Assche
2020-07-31  8:00       ` Can Guo
2020-07-31 16:51         ` Bart Van Assche
2020-07-31 23:17           ` Can Guo
2020-08-03  3:00             ` Stanley Chu [this message]
2020-08-03  5:14               ` Can Guo
2020-08-03  5:27                 ` Stanley Chu
2020-08-03  3:12             ` Bart Van Assche
2020-08-03  5:07               ` Can Guo
2020-08-04 10:01 ` Can Guo

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