On Tue, July 09, 2013, Sujit Reddy Thumma wrote:
> There is a possible race condition in the hardware when the abort
> command is issued to terminate the ongoing SCSI command as described
> below:
>
> - A bit in the door-bell register is set in the controller for a
> new SCSI command.
> - In some rare situations, before controller get a chance to issue
> the command to the device, the software issued an abort command.
It's interesting.
I wonder when we can meet this situation.
Is it possible if SCSI mid layer should send abort command as soon as the
transfer command is issued?
AFAIK abort command is followed if one command has timed out.
That means command have been already issued and no response?
If you had some problem, could you share?
> - If the device recieves abort command first then it returns success
receives
> because the command itself is not present.
> - Now if the controller commits the command to device it will be
> processed.
> - Software thinks that command is aborted and proceed while still
> the device is processing it.
> - The software, controller and device may go out of sync because of
> this race condition.
>
> To avoid this, query task presence in the device before sending abort
> task command so that after the abort operation, the command is guaranteed
> to be non-existent in both controller and the device.
>
> Signed-off-by: Sujit Reddy Thumma <sthu...@codeaurora.org>
> ---
> drivers/scsi/ufs/ufshcd.c | 70 +++++++++++++++++++++++++++++++++++---------
> 1 files changed, 55 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index a176421..51ce096 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -2550,6 +2550,12 @@ static int ufshcd_host_reset(struct scsi_cmnd *cmd)
> * ufshcd_abort - abort a specific command
> * @cmd: SCSI command pointer
> *
> + * Abort the pending command in device by sending UFS_ABORT_TASK task
> management
> + * command, and in host controller by clearing the door-bell register. There
> can
> + * be race between controller sending the command to the device while abort
> is
> + * issued. To avoid that, first issue UFS_QUERY_TASK to check if the command
> is
> + * really issued and then try to abort it.
> + *
> * Returns SUCCESS/FAILED
> */
> static int ufshcd_abort(struct scsi_cmnd *cmd)
> @@ -2558,7 +2564,8 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
> struct ufs_hba *hba;
> unsigned long flags;
> unsigned int tag;
> - int err;
> + int err = 0;
> + int poll_cnt;
> u8 resp;
> struct ufshcd_lrb *lrbp;
>
> @@ -2566,33 +2573,59 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
> hba = shost_priv(host);
> tag = cmd->request->tag;
>
> - spin_lock_irqsave(host->host_lock, flags);
> + /* If command is already aborted/completed, return SUCCESS */
> + if (!(test_bit(tag, &hba->outstanding_reqs)))
> + goto out;
>
> - /* check if command is still pending */
> - if (!(test_bit(tag, &hba->outstanding_reqs))) {
> - err = FAILED;
> - spin_unlock_irqrestore(host->host_lock, flags);
> + lrbp = &hba->lrb[tag];
> + for (poll_cnt = 100; poll_cnt; poll_cnt--) {
> + err = ufshcd_issue_tm_cmd(hba, lrbp->lun, lrbp->task_tag,
> + UFS_QUERY_TASK, &resp);
> + if (!err && resp == UPIU_TASK_MANAGEMENT_FUNC_SUCCEEDED) {
> + /* cmd pending in the device */
> + break;
> + } else if (!err && resp == UPIU_TASK_MANAGEMENT_FUNC_COMPL) {
> + u32 reg;
> +
> + /*
> + * cmd not pending in the device, check if it is
> + * in transition.
> + */
> + reg = ufshcd_readl(hba, REG_UTP_TRANSFER_REQ_DOOR_BELL);
> + if (reg & (1 << tag)) {
> + /* sleep for max. 2ms to stabilize */
> + usleep_range(1000, 2000);
> + continue;
> + }
> + /* command completed already */
> + goto out;
> + } else {
> + if (!err)
> + err = resp; /* service response error */
> + goto out;
> + }
> + }
> +
> + if (!poll_cnt) {
> + err = -EBUSY;
> goto out;
> }
> - spin_unlock_irqrestore(host->host_lock, flags);
>
> - lrbp = &hba->lrb[tag];
> err = ufshcd_issue_tm_cmd(hba, lrbp->lun, lrbp->task_tag,
> UFS_ABORT_TASK, &resp);
> if (err || resp != UPIU_TASK_MANAGEMENT_FUNC_COMPL) {
> - err = FAILED;
> + if (!err)
> + err = resp; /* service response error */
> goto out;
> - } else {
> - err = SUCCESS;
> }
>
> + err = ufshcd_clear_cmd(hba, tag);
> + if (err)
> + goto out;
> +
> scsi_dma_unmap(cmd);
>
> spin_lock_irqsave(host->host_lock, flags);
> -
> - /* clear the respective UTRLCLR register bit */
> - ufshcd_utrl_clear(hba, tag);
> -
> __clear_bit(tag, &hba->outstanding_reqs);
> hba->lrb[tag].cmd = NULL;
> spin_unlock_irqrestore(host->host_lock, flags);
> @@ -2600,6 +2633,13 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
> clear_bit_unlock(tag, &hba->lrb_in_use);
> wake_up(&hba->dev_cmd.tag_wq);
> out:
> + if (!err) {
> + err = SUCCESS;
> + } else {
> + dev_err(hba->dev, "%s: failed with err %d\n", __func__, err);
> + err = FAILED;
> + }
> +
> return err;
> }
>
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation.
>
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