On 10/7/19 10:45 PM, Ewan D. Milne wrote:
> See below.
>
> On Mon, 2019-10-07 at 15:57 +0200, Hannes Reinecke wrote:
>> From: Hannes Reinecke <hare@xxxxxxxx>
>>
>> Some arrays are not capable of returning RTPG data during state
>> transitioning, but rather return an 'LUN not accessible, asymmetric
>> access state transition' sense code. In these cases we
>> can set the state to 'transitioning' directly and don't need to
>> evaluate the RTPG data (which we won't have anyway).
>>
>> Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
>> ---
>> drivers/scsi/device_handler/scsi_dh_alua.c | 21 ++++++++++++++++-----
>> 1 file changed, 16 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
>> index 4971104b1817..f32da0ca529e 100644
>> --- a/drivers/scsi/device_handler/scsi_dh_alua.c
>> +++ b/drivers/scsi/device_handler/scsi_dh_alua.c
>> @@ -512,6 +512,7 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
>> unsigned int tpg_desc_tbl_off;
>> unsigned char orig_transition_tmo;
>> unsigned long flags;
>> + bool transitioning_sense = false;
>>
>> if (!pg->expiry) {
>> unsigned long transition_tmo = ALUA_FAILOVER_TIMEOUT * HZ;
>> @@ -572,13 +573,19 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
>> goto retry;
>> }
>> /*
>> - * Retry on ALUA state transition or if any
>> - * UNIT ATTENTION occurred.
>> + * If the array returns with 'ALUA state transition'
>> + * sense code here it cannot return RTPG data during
>> + * transition. So set the state to 'transitioning' directly.
>> */
>> if (sense_hdr.sense_key == NOT_READY &&
>> - sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a)
>> - err = SCSI_DH_RETRY;
>> - else if (sense_hdr.sense_key == UNIT_ATTENTION)
>> + sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a) {
>> + transitioning_sense = true;
>> + goto skip_rtpg;
>> + }
>> + /*
>> + * Retry on any other UNIT ATTENTION occurred.
>> + */
>> + if (sense_hdr.sense_key == UNIT_ATTENTION)
>> err = SCSI_DH_RETRY;
>> if (err == SCSI_DH_RETRY &&
>> pg->expiry != 0 && time_before(jiffies, pg->expiry)) {
>> @@ -666,7 +673,11 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
>> off = 8 + (desc[7] * 4);
>> }
>>
>> + skip_rtpg:
>> spin_lock_irqsave(&pg->lock, flags);
>> + if (transitioning_sense)
>> + pg->state = SCSI_ACCESS_STATE_TRANSITIONING;
>> +
>> sdev_printk(KERN_INFO, sdev,
>> "%s: port group %02x state %c %s supports %c%c%c%c%c%c%c\n",
>> ALUA_DH_NAME, pg->group_id, print_alua_state(pg->state),
>
> The patch itself looks OK, but I was wondering about a couple of things:
>
> - There are other places in scsi_dh_alua where the ASC/ASCQ 04 0A is checked
> and we retry, I understand that this is a particular case you are solving
> but is the changing of the state to -> transitioning (because that's what
> the device said the state was) applicable in those other cases?
No. The original code was built around the assumption that RTPG would
return the status of the device; consequently we would have to retry
RTPG until we get a final status. But as mentioned, there are arrays
which cannot return RTPG data during transitioning, so the code would
never be able to detect a transitioning state.
With this patch we set the state directly once the said sense code is
received.
But this applies _only_ to the RTPG command, as this is required to move
the state machine along.
None of the other commands are affected.
> - The code originally seems to have been under the assumption that the
> transitioning state was a transient event, so the retry would pick up
> the eventual state. Now, some storage arrays spend a long time in the
> transitioning state, but if we don't send another command are we going to
> get the sense (or the UA) that triggers entry to the eventual ALUA state?
>
Note, there are two types of retries.
The one is the 'normal' command retry, where we resend a command a given
number of times to retrieve the final status.
This is precisely the error which caused this patch.
And then there is a scheduled retry; here we essentially poll the array
with sending RTPG in regular intervals until the 'transitioning' state
is gone. (Check for 'alua_rtpg()' and the handling of the SCSI_DH_RETRY
return value). With the patch we continue to trigger that second type of
retries, which will eventually clear the transitioning state.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 247165 (AG München), GF: Felix Imendörffer
