Re: [PATCH V5 2/3] scsi: ufs: Fix a race condition between ufshcd_abort and eh_work

[Can Guo <cang@codeaurora.org>]

On 2020-12-02 16:48, Stanley Chu wrote:
> Hi Can,
> 
> On Wed, 2020-12-02 at 00:24 -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@codeaurora.org>
>> Signed-off-by: Can Guo <cang@codeaurora.org>
>> ---
>>  drivers/scsi/ufs/ufshcd.c | 55 
>> ++++++++++++++++++++++++++++++++++++-----------
>>  drivers/scsi/ufs/ufshcd.h |  2 ++
>>  2 files changed, 45 insertions(+), 12 deletions(-)
>> 
>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> index f0bb3fc..fa90e15 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");
>> 
>> @@ -4932,6 +4946,7 @@ static void __ufshcd_transfer_req_compl(struct 
>> ufs_hba *hba,
>> 
>>  	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) {
>> @@ -6374,8 +6389,12 @@ 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 +6466,7 @@ 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 +6716,6 @@ 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 +6736,7 @@ 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 +6755,27 @@ 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));
> 
> The timed out "tag" is cleared once here.
> 
>> +			__set_bit(tag, &hba->outstanding_reqs);
>> +			lrbp->in_use = true;
>> +			hba->force_reset = true;
>> +			ufshcd_schedule_eh_work(hba);
> 
> The same "tag" would be cleared again in error handler with
> __ufshcd_transfer_req_compl().
> 
> In __ufshcd_transfer_req_compl, hba->clk_scaling.active_reqs will be
> decreased if clk-scaling is supported as below,
> 
> 	if (ufshcd_is_clkscaling_supported(hba))
> 		hba->clk_scaling.active_reqs--;
> 
> Will be the hba->clk_scaling.active_reqs value become abnormal by this
> flow?
> 

Yes, it may undershoot. Actually the logic in 
__ufshcd_transfer_req_compl()
should be updated - clk_scaling.active_reqs should be updated only when
there are cmds (scsi or query) to complete. Here is not the only place 
which
can cause a undershoot. We can prevent the undershoot with below check.

  	if (ufshcd_is_clkscaling_supported(hba) &&
             hba->clk_scaling.active_reqs > 0)
  		hba->clk_scaling.active_reqs--;

Thanks,

Can Guo.

> Thanks,
> Stanley Chu
> 
>> +		}
>> +		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;
>>  };
>> 
>>  /**