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.
> Secondly this path fails with 'directio' multipath checker. Remember that 'directio'
> is using 'fs' requests, not block-pc ones. Hence for all I/O the prep_fn() callback
> is evaluated, which will return 'DEFER' here once the path is in transitioning.
> And the state is never updated as RTPG is never called.
Testing ALUA with directio path checker did not result in such immutable
state in the few instances that TPGS_STATE_TRANSITIONING was seen in
alua_prep_fn.
> I'm currently preparing a patch which addressed these situations, too.
OK, please share.
Thanks,
Mike
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