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.
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.
I'm currently preparing a patch which addressed these situations, too.
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@xxxxxxx +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)
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