Re: scsi_dh_alua: add missing transitioning state support

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On 09/20/2010 09:27 PM, Mike Christie 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.

Did we want to move this check to the block layer btw? If so it could solve the problem.

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