linux-kernel - Re: [PATCH v1 2/3] scsi: ufs: Optimize host lock on transfer requests send/compl paths

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Message-ID: <a29164e1-ab7d-6dbc-0fb9-029f203de735@acm.org>
Date:   Wed, 16 Jun 2021 19:49:01 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Can Guo <cang@...eaurora.org>, asutoshd@...eaurora.org,
        nguyenb@...eaurora.org, hongwus@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com
Cc:     Stanley Chu <stanley.chu@...iatek.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Bean Huo <beanhuo@...ron.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v1 2/3] scsi: ufs: Optimize host lock on transfer requests
 send/compl paths

On 5/24/21 1:36 AM, Can Guo wrote:
> @@ -2688,6 +2705,43 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
> +	case UFSHCD_STATE_EH_SCHEDULED_FATAL:
> +		/*
> +		 * pm_runtime_get_sync() is used at error handling preparation
> +		 * stage. If a scsi cmd, e.g. the SSU cmd, is sent from hba's
> +		 * PM ops, it can never be finished if we let SCSI layer keep
> +		 * retrying it, which gets err handler stuck forever. Neither
> +		 * can we let the scsi cmd pass through, because UFS is in bad
> +		 * state, the scsi cmd may eventually time out, which will get
> +		 * err handler blocked for too long. So, just fail the scsi cmd
> +		 * sent from PM ops, err handler can recover PM error anyways.
> +		 */
> +		if (hba->pm_op_in_progress) {
> +			hba->force_reset = true;
> +			set_host_byte(cmd, DID_BAD_TARGET);
> +			cmd->scsi_done(cmd);
> +			goto out;
> +		}
> +		fallthrough;

Hi Can,

I know that this patch only moves the above code and that the above code
has not been introduced by this patch. Anyway, is my understanding
correct that ufshcd_err_handler() can change the host controller state
from UFSHCD_STATE_EH_SCHEDULED_FATAL into UFSHCD_STATE_RESET and next
into UFSHCD_STATE_OPERATIONAL? If so, if the above code completes a READ
with status DID_BAD_TARGET and if recovery by the error handler
succeeds, will that cause the filesystem above the UFS driver to change
into read-only mode? If the above code completes a WRITE with status
DID_BAD_TARGET, will that cause data corruption? Is there any other
solution to prevent data corruption than merging the
UFSHCD_STATE_EH_SCHEDULED_FATAL and UFSHCD_STATE_EH_SCHEDULED_NON_FATAL
back into a single state and changing the ufshcd_rpm_get_sync(hba) call
in ufshcd_err_handling_prepare() into a pm_runtime_get_noresume() call?

Thanks,

Bart.