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

[Hannes Reinecke <hare@suse.de>]

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_ ...).
But yeah, I could see to limit this somewhat.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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