RE: [PATCH v3] scsi: ufs: Cleanup completed request without interrupt notification

Avri Altman
2020-07-09T08:32:01Z

>
> If somehow no interrupt notification is raised for a completed request
> and its doorbell bit is cleared by host, UFS driver needs to cleanup
> its outstanding bit in ufshcd_abort().
Theoretically, this case is already accounted for -
See line 6407: a proper error is issued and eventually outstanding req is cleared.

Can you go over the scenario you are attending line by line,
And explain why ufshcd_abort does not account for it?

>
> Otherwise, system may crash by below abnormal flow:
>
> After this request is requeued by SCSI layer with its
> outstanding bit set, the next completed request will trigger
> ufshcd_transfer_req_compl() to handle all "completed outstanding
> bits". In this time, the "abnormal outstanding bit" will be detected
> and the "requeued request" will be chosen to execute request
> post-processing flow. This is wrong and blk_finish_request() will
> BUG_ON because this request is still "alive".
>
> It is worth mentioning that before ufshcd_abort() cleans the timed-out
> request, driver need to check again if this request is really not
> handled by __ufshcd_transfer_req_compl() yet because it may be
> possible that the interrupt comes very lately before the cleaning.
What do you mean? Why checking the outstanding reqs isn't enough?

>
> Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
> ---
> drivers/scsi/ufs/ufshcd.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 8603b07045a6..f23fb14df9f6 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -6462,7 +6462,7 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
> /* command completed already */
> dev_err(hba->dev, "%s: cmd at tag %d successfully cleared from
> DB.\n",
> __func__, tag);
> - goto out;
> + goto cleanup;
But you've arrived here only if (!(test_bit(tag, &hba->outstanding_reqs))) -
See line 6400.

> } else {
> dev_err(hba->dev,
> "%s: no response from device. tag = %d, err %d\n",
> @@ -6496,9 +6496,14 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
> goto out;
> }
>
> +cleanup:
> + spin_lock_irqsave(host->host_lock, flags);
> + if (!test_bit(tag, &hba->outstanding_reqs)) {
> + spin_unlock_irqrestore(host->host_lock, flags);
> + goto out;
> + }
> scsi_dma_unmap(cmd);
>
> - spin_lock_irqsave(host->host_lock, flags);
> ufshcd_outstanding_req_clear(hba, tag);
> hba->lrb[tag].cmd = NULL;
> spin_unlock_irqrestore(host->host_lock, flags);
> --
> 2.18.0