Re: [PATCH] sd: always retry READ CAPACITY for ALUA state transition

[Martin George <marting@netapp.com>]

On 4/30/2015 5:56 PM, Hannes Reinecke wrote:
> On 04/28/2015 11:18 PM, James Bottomley wrote:
>> On Mon, 2015-04-27 at 11:35 +0200, Hannes Reinecke wrote:
>>> During ALUA state transitions the device might return
>>> a sense code 02/04/0a (Logical unit not accessible, asymmetric
>>> access state transition). As this is a transient error
>>> we should just retry the READ CAPACITY call until
>>> the state transition finishes and the correct
>>> capacity can be returned.
>>>
>>> Signed-off-by: Hannes Reinecke <hare@suse.de>
>>> ---
>>>   drivers/scsi/sd.c | 10 ++++++++++
>>>   1 file changed, 10 insertions(+)
>>>
>>> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
>>> index 79beebf..7178b05 100644
>>> --- a/drivers/scsi/sd.c
>>> +++ b/drivers/scsi/sd.c
>>> @@ -1987,6 +1987,11 @@ static int read_capacity_16(struct scsi_disk *sdkp, struct scsi_device *sdp,
>>>   				 * give it one more chance */
>>>   				if (--reset_retries > 0)
>>>   					continue;
>>> +			if (sense_valid &&
>>> +			    sshdr.sense_key == NOT_READY &&
>>> +			    sshdr.asc == 0x04 && sshdr.ascq == 0x0A)
>>> +				/* ALUA state transition; always retry */
>>> +				continue;
>>>   		}
>>>   		retries--;
>>>
>>> @@ -2069,6 +2074,11 @@ static int read_capacity_10(struct scsi_disk *sdkp, struct scsi_device *sdp,
>>>   				 * give it one more chance */
>>>   				if (--reset_retries > 0)
>>>   					continue;
>>> +			if (sense_valid &&
>>> +			    sshdr.sense_key == NOT_READY &&
>>> +			    sshdr.asc == 0x04 && sshdr.ascq == 0x0A)
>>> +				/* ALUA state transition; always retry */
>>> +				continue;
>>>   		}
>>>   		retries--;
>>>
>>
>> Got to say I really don't like this infinite retry possibility.  How
>> long does the ALUA transition take?  Would increasing retries work (or
>> even hijacking reset_retries)?
>>
> Well ... transitioning could be quite long (NetApp FAS has a
> transition timeout of 30 _minutes_ ...).

Well, actually NetApp FAS has a transition timeout of 2 minutes, and not 
30 minutes - as reported in the IMPLICIT TRANSITION TIMEOUT value in the 
extended RTPG data.

-Martin