On 11/11/22 20:09, Niklas Cassel wrote:
> A NCQ error means that the device has aborted a single NCQ command and
> halted further processing of queued commands.
Nit: To be strict with wording, this should say something like "an NCQ
command failure results in the device aborting the execution of all active
commands."
> To get the single NCQ command that caused the NCQ error, host software has
> to read the NCQ error log, which also takes the device out of error state.
>
> When the device encounters a NCQ error, we receive an error interrupt from
> the HBA, and call ata_do_link_abort() to mark all outstanding commands on
> the link as ATA_QCFLAG_FAILED (which means that these commands are owned
> by libata EH), and then call ata_qc_complete() on them.
>
> ata_qc_complete() will call fill_result_tf() for all commands marked as
> ATA_QCFLAG_FAILED.
>
> The taskfile is simply the latest status/error as seen from the device's
> perspective. The taskfile will have ATA_ERR set in the status field and
> ATA_ABORTED set in the error field.
>
> When we fill the current taskfile values for all outstanding commands,
> that means that qc->result_tf will have ATA_ERR set for all commands
> owned by libata EH.
>
> When ata_eh_link_autopsy() later analyzes all commands owned by libata EH,
> it will call ata_eh_analyze_tf(), which will check if qc->result_tf has
> ATA_ERR set, if it does, it will set qc->err_mask (which marks the command
> as an error).
>
> When ata_eh_finish() later calls __ata_qc_complete() on all commands owned
> by libata EH, it will call qc->complete_fn() (ata_scsi_qc_complete()),
> ata_scsi_qc_complete() will call ata_gen_ata_sense() to generate sense
> data if qc->err_mask is set.
>
> This means that we will generate sense data for commands that really
> should not have any sense data set. Having sense data set might cause SCSI
> to finish these commands instead of retrying them.
>
> While this incorrect behavior has existed for a long time, this first
> became a problem once we started reading the correct taskfile register in
> commit 4ba09d202657 ("ata: libahci: read correct status and error field
> for NCQ commands").
>
> Before this commit, NCQ commands would read the taskfile values received
> from the last non-NCQ command completion, which most likely did not have
> ATA_ERR set, since the last non-NCQ command was most likely not an error.
>
> Fix this by clearing ATA_ERR and any error bits for all commands except
> the actual command that caused the NCQ error, since the error bits in the
> taskfile are not applicable to them.
>
> Fixes: 4ba09d202657 ("ata: libahci: read correct status and error field for NCQ commands")
> Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxx>
> ---
> drivers/ata/libata-sata.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
> index 283ce1ab29cf..6b2dcf3eb2fb 100644
> --- a/drivers/ata/libata-sata.c
> +++ b/drivers/ata/libata-sata.c
> @@ -1476,6 +1476,25 @@ void ata_eh_analyze_ncq_error(struct ata_link *link)
> }
> }
>
> + ata_qc_for_each_raw(ap, qc, tag) {
> + if (!(qc->flags & ATA_QCFLAG_FAILED) ||
> + ata_dev_phys_link(qc->dev) != link)
> + continue;
> +
> + /* Skip the single QC which caused the NCQ error. */
> + if (qc->err_mask)
> + continue;
Before the continue, should we check that this qc tag is the one we got
from ata_eh_read_log_10h() ? We should at least warn if there is a mismatch.
> +
> + /*
> + * For SATA, the STATUS and ERROR fields are shared for all NCQ
> + * commands that were completed with the same SDB FIS.
> + * Therefore, we have to clear the ATA_ERR bit for all QCs
> + * except the one that caused the NCQ error.
> + */
> + qc->result_tf.status &= ~ATA_ERR;
> + qc->result_tf.error = 0;
> + }
> +
> ehc->i.err_mask &= ~AC_ERR_DEV;
> }
> EXPORT_SYMBOL_GPL(ata_eh_analyze_ncq_error);
--
Damien Le Moal
Western Digital Research
