Flood of SCSI retries when a port is in transitioning

[Hannes Reinecke <hare@suse.de>]

Hi all,

our friends from NetApp discovered a SCSI retry flood when a remote 
port is in ALUA 'transitioning' state.

The device will then return
Not ready/LUN Not Accessible - ALUA state transition
which will be evaluated in scsi_dh_alua.c:alua_check_sense()
as ADD_TO_MLQUEUE.
This will cause an immediate retry of the command and hence the 
target will be pounded with a flood of retries.

I have now tried to alleviate this by returning 'NEEDS_RETRY',

--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -451,7 +451,7 @@ static int alua_check_sense(struct scsi_device 
*sdev,
                         /*
                          * LUN Not Accessible - ALUA state transition
                          */
-                       return ADD_TO_MLQUEUE;
+                       return NEEDS_RETRY;
                 if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0b)
                         /*
                          * LUN Not Accessible -- Target port in 
standby state

but then the command will be aborted after the retry count has been 
exhausted. Which will then cause I/O errors. Also not good.
Is there a way of forcing a delayed retry, like BLKPREP_DEFER does?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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