On Mon, Sep 20 2010 at 10:27pm -0400,
Mike Christie <michaelc@xxxxxxxxxxx> wrote:
> On 09/20/2010 10:35 AM, Mike Snitzer wrote:
> >Hi Hannes,
> >
> >On Tue, Aug 31 2010 at 11:11am -0400,
> >Mike Snitzer<snitzer@xxxxxxxxxx> wrote:
> >
> >>On Mon, Aug 30 2010 at 5:36am -0400,
> >>Hannes Reinecke<hare@xxxxxxx> wrote:
> >>
> >>>Nicholas A. Bellinger wrote:
> >>>>On Tue, 2010-08-17 at 15:05 -0400, Mike Snitzer wrote:
> >>>>>Handle transitioning in the prep_fn.
> >>>>>Handle transitioning in alua_rtpg's implicit alua code too.
> >>>>>
> >>>>>These gaps were identified during controller failover testing of an
> >>>>>ALUA array.
> >>>>>
> >>>>>Signed-off-by: Mike Snitzer<snitzer@xxxxxxxxxx>
> >>>>>---
> >>>>> drivers/scsi/device_handler/scsi_dh_alua.c | 10 +++++++---
> >>>>> 1 files changed, 7 insertions(+), 3 deletions(-)
> >>>>>
> >>>>>diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
> >>>>>index 1a970a7..c1eedc5 100644
> >>>>>--- a/drivers/scsi/device_handler/scsi_dh_alua.c
> >>>>>+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
> >>>>>@@ -616,6 +616,9 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_dh_data *h)
> >>>>> h->state == TPGS_STATE_STANDBY)
> >>>>> /* Useable path if active */
> >>>>> err = SCSI_DH_OK;
> >>>>>+ else if (h->state == TPGS_STATE_TRANSITIONING)
> >>>>>+ /* State transition, retry */
> >>>>>+ goto retry;
> >>>>> else
> >>>>> /* Path unuseable for unavailable/offline */
> >>>>> err = SCSI_DH_DEV_OFFLINED;
> >>>>>@@ -698,13 +701,14 @@ static int alua_prep_fn(struct scsi_device *sdev, struct request *req)
> >>>>> struct alua_dh_data *h = get_alua_data(sdev);
> >>>>> int ret = BLKPREP_OK;
> >>>>>
> >>>>>- if (h->state != TPGS_STATE_OPTIMIZED&&
> >>>>>- h->state != TPGS_STATE_NONOPTIMIZED) {
> >>>>>+ if (h->state == TPGS_STATE_TRANSITIONING)
> >>>>>+ ret = BLKPREP_DEFER;
> >>>>>+ else if (h->state != TPGS_STATE_OPTIMIZED&&
> >>>>>+ h->state != TPGS_STATE_NONOPTIMIZED) {
> >>>>> ret = BLKPREP_KILL;
> >>>>> req->cmd_flags |= REQ_QUIET;
> >>>>> }
> >>>>> return ret;
> >>>>>-
> >>>>> }
> >>>>>
> >>>>
> >>>>Makes sense to me..
> >>>>
> >>>>Acked-by: Nicholas A. Bellinger<nab@xxxxxxxxxxxxxxx>
> >>>>
> >>>Not so fast. There are two problems with this approach:
> >>>
> >>>The path is retried indefinitely. Arrays are _supposed_ to be in 'transitioning'
> >>>only temporary; however, if the array is stuck due to a fw error we're stuck in 'defer',
> >>>too.
> >>
> >>And what is the problem with that? The IO will eventually time out.
> >
> >To restate as a question: even though we'll retry in alua_rtpg();
> >shouldn't the SCSI command eventually time out (via
> >scsi_attempt_requeue_command)?
>
> That function is only in RHEL. Requests that are prepd and sent to
> the scsi layer and driver would eventually timeout in
> scsi_softirq_done in upstream.
>
> alua_prep_fn prevents the IO from getting sent to the scsi layer so
> we do not hit the check in scsi_softirq_done though.
That is only the case if alua_prep_fn were to return BLKPREP_DEFER
right?
Taking a step back:
1) the proposed alua_prep_fn BLKPREP_DEFER change is not correct and is
no longer being proposed...
2) the patch also modified alua_rtpg() so implicit ALUA would retry
(just like explicit ALUA currently does) if TPGS_STATE_TRANSITIONING
- so why should we avoid retry for implicit but do it for explicit?
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