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)?
Note that my proposed change to alua_rtpg() just adds a
TPGS_STATE_TRANSITIONING handler for implicit ALUA -- explicit ALUA
already has such a handler.
Allowing implicit ALUA to fall through (as we do currently) causes a
return alua_rtpg() of SCSI_DH_DEV_OFFLINED -- which isn't the correct
state.
> > 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 had another look and I see what you're saying. Thanks for catching this!
> > I'm currently preparing a patch which addressed these situations, too.
>
> OK, please share.
Do you have that patch you were preparing? I look forward to seeing
your solution to this.
Thanks,
Mike
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