From: Bart Van Assche <bvanassche@acm.org>
To: Can Guo <cang@codeaurora.org>
Cc: Stanley Chu <stanley.chu@mediatek.com>,
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: Fri, 31 Jul 2020 09:51:55 -0700 [thread overview]
Message-ID: <f45c6c47-ffc5-3f8e-3234-9e5989dbf996@acm.org> (raw)
In-Reply-To: <8b0a158a7c3ee2165e09290996521ffc@codeaurora.org>
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.
next prev parent reply other threads:[~2020-07-31 16:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-24 14:02 [PATCH v4] scsi: ufs: Cleanup completed request without interrupt notification 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 [this message]
2020-07-31 23:17 ` Can Guo
2020-08-03 3:00 ` Stanley Chu
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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