Message-ID: <843a2bb60b16929239ac5ee100bac465@codeaurora.org>
Date:   Thu, 03 Dec 2020 13:11:39 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, rnayak@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        saravanak@...gle.com, salyzyn@...gle.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>,
        Bean Huo <beanhuo@...ron.com>,
        Bart Van Assche <bvanassche@....org>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V7 2/3] scsi: ufs: Fix a race condition between
 ufshcd_abort and eh_work

On 2020-12-03 12:51, Stanley Chu wrote:
> On Thu, 2020-12-03 at 12:01 +0800, Can Guo wrote:
>> On 2020-12-03 10:21, Stanley Chu wrote:
>> > On Wed, 2020-12-02 at 04:04 -0800, Can Guo wrote:
>> >> In current task abort routine, if task abort happens to the device
>> >> W-LU,
>> >> the code directly jumps to ufshcd_eh_host_reset_handler() to perform a
>> >> full reset and restore then returns FAIL or SUCCESS. Commands sent to
>> >> the
>> >> device W-LU are most likely the SSU cmds sent during UFS PM
>> >> operations. If
>> >> such SSU cmd enters task abort routine, when
>> >> ufshcd_eh_host_reset_handler()
>> >> flushes eh_work, it will get stuck there since err_handler is
>> >> serialized
>> >> with PM operations.
>> >>
>> >> In order to unblock above call path, we merely clean up the lrb taken
>> >> by
>> >> this cmd, queue the eh_work and return SUCCESS. Once the cmd is
>> >> aborted,
>> >> the PM operation which sends out the cmd just errors out, then
>> >> err_handler
>> >> shall be able to proceed with the full reset and restore.
>> >>
>> >> In this scenario, the cmd is aborted even before it is actually
>> >> cleared by
>> >> HW, set the lrb->in_use flag to prevent subsequent cmds, including
>> >> SCSI
>> >> cmds and dev cmds, from taking the lrb released from abort. The flag
>> >> shall
>> >> evetually be cleared in __ufshcd_transfer_req_compl() invoked by the
>> >> full
>> >> reset and restore from err_handler.
>> >>
>> >> Reviewed-by: Asutosh Das <asutoshd@...eaurora.org>
>> >> Signed-off-by: Can Guo <cang@...eaurora.org>
>> >> ---
>> >>  drivers/scsi/ufs/ufshcd.c | 60
>> >> +++++++++++++++++++++++++++++++++++++----------
>> >>  drivers/scsi/ufs/ufshcd.h |  2 ++
>> >>  2 files changed, 49 insertions(+), 13 deletions(-)
>> >>
>> >> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> >> index f0bb3fc..26c1fa0 100644
>> >> --- a/drivers/scsi/ufs/ufshcd.c
>> >> +++ b/drivers/scsi/ufs/ufshcd.c
>> >> @@ -2539,6 +2539,14 @@ static int ufshcd_queuecommand(struct Scsi_Host
>> >> *host, struct scsi_cmnd *cmd)
>> >>  		(hba->clk_gating.state != CLKS_ON));
>> >>
>> >>  	lrbp = &hba->lrb[tag];
>> >> +	if (unlikely(lrbp->in_use)) {
>> >> +		if (hba->pm_op_in_progress)
>> >> +			set_host_byte(cmd, DID_BAD_TARGET);
>> >> +		else
>> >> +			err = SCSI_MLQUEUE_HOST_BUSY;
>> >> +		ufshcd_release(hba);
>> >> +		goto out;
>> >> +	}
>> >>
>> >>  	WARN_ON(lrbp->cmd);
>> >>  	lrbp->cmd = cmd;
>> >> @@ -2781,6 +2789,11 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba
>> >> *hba,
>> >>
>> >>  	init_completion(&wait);
>> >>  	lrbp = &hba->lrb[tag];
>> >> +	if (unlikely(lrbp->in_use)) {
>> >> +		err = -EBUSY;
>> >> +		goto out;
>> >> +	}
>> >> +
>> >>  	WARN_ON(lrbp->cmd);
>> >>  	err = ufshcd_compose_dev_cmd(hba, lrbp, cmd_type, tag);
>> >>  	if (unlikely(err))
>> >> @@ -2797,6 +2810,7 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba
>> >> *hba,
>> >>
>> >>  	err = ufshcd_wait_for_dev_cmd(hba, lrbp, timeout);
>> >>
>> >> +out:
>> >>  	ufshcd_add_query_upiu_trace(hba, tag,
>> >>  			err ? "query_complete_err" : "query_complete");
>> >>
>> >> @@ -4929,9 +4943,11 @@ static void __ufshcd_transfer_req_compl(struct
>> >> ufs_hba *hba,
>> >>  	struct scsi_cmnd *cmd;
>> >>  	int result;
>> >>  	int index;
>> >> +	bool update_scaling = false;
>> >>
>> >>  	for_each_set_bit(index, &completed_reqs, hba->nutrs) {
>> >>  		lrbp = &hba->lrb[index];
>> >> +		lrbp->in_use = false;
>> >>  		lrbp->compl_time_stamp = ktime_get();
>> >>  		cmd = lrbp->cmd;
>> >>  		if (cmd) {
>> >> @@ -4944,15 +4960,17 @@ static void __ufshcd_transfer_req_compl(struct
>> >> ufs_hba *hba,
>> >>  			/* Do not touch lrbp after scsi done */
>> >>  			cmd->scsi_done(cmd);
>> >>  			__ufshcd_release(hba);
>> >> +			update_scaling = true;
>> >>  		} else if (lrbp->command_type == UTP_CMD_TYPE_DEV_MANAGE ||
>> >>  			lrbp->command_type == UTP_CMD_TYPE_UFS_STORAGE) {
>> >>  			if (hba->dev_cmd.complete) {
>> >>  				ufshcd_add_command_trace(hba, index,
>> >>  						"dev_complete");
>> >>  				complete(hba->dev_cmd.complete);
>> >> +				update_scaling = true;
>> >>  			}
>> >>  		}
>> >> -		if (ufshcd_is_clkscaling_supported(hba))
>> >> +		if (ufshcd_is_clkscaling_supported(hba) && update_scaling)
>> >>  			hba->clk_scaling.active_reqs--;
>> >>  	}
>> >>
>> >> @@ -6374,8 +6392,12 @@ static int ufshcd_issue_devman_upiu_cmd(struct
>> >> ufs_hba *hba,
>> >>
>> >>  	init_completion(&wait);
>> >>  	lrbp = &hba->lrb[tag];
>> >> -	WARN_ON(lrbp->cmd);
>> >> +	if (unlikely(lrbp->in_use)) {
>> >> +		err = -EBUSY;
>> >> +		goto out;
>> >> +	}
>> >>
>> >> +	WARN_ON(lrbp->cmd);
>> >>  	lrbp->cmd = NULL;
>> >>  	lrbp->sense_bufflen = 0;
>> >>  	lrbp->sense_buffer = NULL;
>> >> @@ -6447,6 +6469,7 @@ static int ufshcd_issue_devman_upiu_cmd(struct
>> >> ufs_hba *hba,
>> >>  		}
>> >>  	}
>> >>
>> >> +out:
>> >>  	blk_put_request(req);
>> >>  out_unlock:
>> >>  	up_read(&hba->clk_scaling_lock);
>> >> @@ -6696,16 +6719,6 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
>> >>  		BUG();
>> >>  	}
>> >>
>> >> -	/*
>> >> -	 * Task abort to the device W-LUN is illegal. When this command
>> >> -	 * will fail, due to spec violation, scsi err handling next step
>> >> -	 * will be to send LU reset which, again, is a spec violation.
>> >> -	 * To avoid these unnecessary/illegal step we skip to the last error
>> >> -	 * handling stage: reset and restore.
>> >> -	 */
>> >> -	if (lrbp->lun == UFS_UPIU_UFS_DEVICE_WLUN)
>> >> -		return ufshcd_eh_host_reset_handler(cmd);
>> >> -
>> >>  	ufshcd_hold(hba, false);
>> >>  	reg = ufshcd_readl(hba, REG_UTP_TRANSFER_REQ_DOOR_BELL);
>> >>  	/* If command is already aborted/completed, return SUCCESS */
>> >> @@ -6726,7 +6739,7 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
>> >>  	 * to reduce repeated printouts. For other aborted requests only
>> >> print
>> >>  	 * basic details.
>> >>  	 */
>> >> -	scsi_print_command(hba->lrb[tag].cmd);
>> >> +	scsi_print_command(cmd);
>> >>  	if (!hba->req_abort_count) {
>> >>  		ufshcd_update_reg_hist(&hba->ufs_stats.task_abort, 0);
>> >>  		ufshcd_print_host_regs(hba);
>> >> @@ -6745,6 +6758,27 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
>> >>  		goto cleanup;
>> >>  	}
>> >>
>> >> +	/*
>> >> +	 * Task abort to the device W-LUN is illegal. When this command
>> >> +	 * will fail, due to spec violation, scsi err handling next step
>> >> +	 * will be to send LU reset which, again, is a spec violation.
>> >> +	 * To avoid these unnecessary/illegal steps, first we clean up
>> >> +	 * the lrb taken by this cmd and mark the lrb as in_use, then
>> >> +	 * queue the eh_work and bail.
>> >> +	 */
>> >> +	if (lrbp->lun == UFS_UPIU_UFS_DEVICE_WLUN) {
>> >> +		spin_lock_irqsave(host->host_lock, flags);
>> >> +		if (lrbp->cmd) {
>> >> +			__ufshcd_transfer_req_compl(hba, (1UL << tag));
>> >> +			__set_bit(tag, &hba->outstanding_reqs);
>> >> +			lrbp->in_use = true;
>> >> +			hba->force_reset = true;
>> >> +			ufshcd_schedule_eh_work(hba);
>> >
>> > ufshcd_schedule_eh_work() will set hba->ufshcd_state as
>> > UFSHCD_STATE_EH_SCHEDULED_FATAL. While in this state,
>> > ufshcd_queuecommand() will set_host_byte(DID_BAD_TARGET) which is
>> > similar as what you would like to do in this patch.
>> >
>> > Is this enough for avoiding reusing tag issue? Just wonder if
>> > lrpb->in_use flag is really required to be added.
>> 
>> Hi Stanley,
>> 
>> Thanks for the discussion.
>> 
>> To be accurate, it is to prevent lrb from being re-used, not the
>> tag.
>> Block layer and/or scsi layer can re-use the tag right after
>> we abort the cmd, but the lrb is empty since we cleared it from
>> abort path and we need to make sure the lrb stays empty before the
>> full reset and restore happens.
> 
> What is the definition of "empty" here?

Yes, it means lrb->cmd is NULL.

> 
> If it means lrb->cmd shall be empty (to not invoking scsi_done again),
> then the hba->ufshcd_state check in ufshcd_queuecommend() will also
> clear the re-used lrb->cmd if ufshcd_state is in
> UFSHCD_STATE_EH_SCHEDULED_FATAL case.

Yes, but that would have a race condition - say a cmd re-uses the tag 
and
occupies the lrb in queuecommand, at the same time the real completion 
IRQ
of previous cmd comes (althrough we aborted it due to it timed out, but 
the
completion IRQ can come at any time before the full reset and restore is
performed), then the new cmd will be wrongly completed by IRQ handler 
from
__ufshcd_transfer_req_compl() which is actually fired by the last cmd, 
so
we need to block it even before the cmd takes the lrb - before

lrbp->cmd = cmd;

> 
> However ufshcd_state cannot protect other paths now, for example,
> ufshcd_exec_dev_cmd(), so lrbp->in_use may be required for this usage,
> or ufshcd_state check can be added to help.
> 
> BTW, would you also need to consider ufshcd_issue_devman_upiu_cmd() 
> that
> is another possible path to re-use lrb?

In this change, there are checks of lrb->in_use in 
ufshcd_queuecommand(),
ufshcd_exec_dev_cmd() and ufshcd_issue_devman_upiu_cmd().

Thanks,

Can Guo.

> 
> Thanks,
> Stanley Chu
> 
>> So, in queuecommand path, we have
>> below checks to prevernt the lrb being re-used. This is before
>> hba->ufshcd_state checks.
>> 
>> +    if (unlikely(lrbp->in_use)) {
>> +        if (hba->pm_op_in_progress)
>> +            set_host_byte(cmd, DID_BAD_TARGET);
>> +        else
>> +            err = SCSI_MLQUEUE_HOST_BUSY;
>> +        ufshcd_release(hba);
>> +        goto out;
>> +    }
>> 
>> In above checks, below exception is for the case that a SSU cmd
>> sent from PM ops is trying to re-use the lrb. In this case, we
>> should simply let it fail so that PM ops errors out to unblock
>> error handling (since error handling is serialized with PM ops).
>> 
>> +        if (hba->pm_op_in_progress)
>> +            set_host_byte(cmd, DID_BAD_TARGET);
>> 
>> Thanks,
>> 
>> Can Guo.
>> 
>> >
>> >> +		}
>> >> +		spin_unlock_irqrestore(host->host_lock, flags);
>> >> +		goto out;
>> >> +	}
>> >> +
>> >>  	/* Skip task abort in case previous aborts failed and report failure
>> >> */
>> >>  	if (lrbp->req_abort_skip)
>> >>  		err = -EIO;
>> >> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
>> >> index 1e680bf..66e5338 100644
>> >> --- a/drivers/scsi/ufs/ufshcd.h
>> >> +++ b/drivers/scsi/ufs/ufshcd.h
>> >> @@ -163,6 +163,7 @@ struct ufs_pm_lvl_states {
>> >>   * @crypto_key_slot: the key slot to use for inline crypto (-1 if
>> >> none)
>> >>   * @data_unit_num: the data unit number for the first block for
>> >> inline crypto
>> >>   * @req_abort_skip: skip request abort task flag
>> >> + * @in_use: indicates that this lrb is still in use
>> >>   */
>> >>  struct ufshcd_lrb {
>> >>  	struct utp_transfer_req_desc *utr_descriptor_ptr;
>> >> @@ -192,6 +193,7 @@ struct ufshcd_lrb {
>> >>  #endif
>> >>
>> >>  	bool req_abort_skip;
>> >> +	bool in_use;
>> >>  };
>> >>
>> >>  /**

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