Re: scsi_dh_alua: add missing transitioning state support

[Hannes Reinecke <hare@suse.de>]

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Mike Snitzer wrote:
> 
> On Wed, Sep 22 2010 at  6:13am -0400,
> Hannes Reinecke <hare@suse.de> wrote:
> 
>> Mike Christie wrote:
>>> On 09/21/2010 02:33 PM, Mike Snitzer wrote:
>>>> 2) the patch also modified alua_rtpg() so implicit ALUA would retry
>>>>     (just like explicit ALUA currently does) if TPGS_STATE_TRANSITIONING
>>>>     - so why should we avoid retry for implicit but do it for explicit?
>>> Leaving that for Hannes. I cannot think of a reason. Probably just did
>>> not do it.
>> Finally I got around to answering this.
>>
>> I've attached a patch which I made the other day which seems to work
>> reasonably well.
>> Looks better from my side, so if you agree I'll be sending it
>> upstream properly.
> 
> Looks good for covering this "2)" change above.
> 
> But "1)" change you had concern with (in my previous patch) was that
> alua_prep_fn would return BLKPREP_DEFER if TPGS_STATE_TRANSITIONING.
> This was bad in that FS requests (like the directio path checker) would
> always call ->prep_fn and that if TPGS_STATE_TRANSITIONING the RTPG
> state would never be reevaluated.. leaving us stuck in BLKPREP_DEFER.
> 
> Seems I'm missing a new flow that proves this is no longer a concern.
> 
The device_handler will keep retrying any path in 'transitioning'.
After ALUA_FAILOVER_TIMEOUT the device handler will either have
updated the port state to something other than 'transitioning' or
returned with 'SCSI_DH_RETRY'.
But yes, you are right; we should be setting the port to something
else than 'transitioning' then. Probably 'standby' is a good choice
here.
New patch attached.

Thanks for the review.

Cheers,

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

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>From db02ba3c33a4a1dbfcdc4de1b73e378f7b3d8925 Mon Sep 17 00:00:00 2001
From: Hannes Reinecke <hare@suse.de>
Date: Wed, 22 Sep 2010 12:09:07 +0200
Subject: [PATCH] scsi_dh_alua: Handle all states correctly

For ALUA we should be handling all states, independent of whether
is explicit or implicit. For 'Transitioning' we should be retry
for a certain amount of time; after that we're setting the port
to 'Standby' and return SCSI_DH_RETRY to signal upper layers
a retry is in order here.

Signed-off-by: Hannes Reinecke <hare@suse.de>

diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index 1a970a7..c7e11ed 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -31,6 +31,7 @@
 #define TPGS_STATE_NONOPTIMIZED		0x1
 #define TPGS_STATE_STANDBY		0x2
 #define TPGS_STATE_UNAVAILABLE		0x3
+#define TPGS_STATE_LBA_DEPENDENT	0x4
 #define TPGS_STATE_OFFLINE		0xe
 #define TPGS_STATE_TRANSITIONING	0xf
 
@@ -39,6 +40,7 @@
 #define TPGS_SUPPORT_NONOPTIMIZED	0x02
 #define TPGS_SUPPORT_STANDBY		0x04
 #define TPGS_SUPPORT_UNAVAILABLE	0x08
+#define TPGS_SUPPORT_LBA_DEPENDENT	0x10
 #define TPGS_SUPPORT_OFFLINE		0x40
 #define TPGS_SUPPORT_TRANSITION		0x80
 
@@ -460,6 +462,8 @@ static char print_alua_state(int state)
 		return 'S';
 	case TPGS_STATE_UNAVAILABLE:
 		return 'U';
+	case TPGS_STATE_LBA_DEPENDENT:
+		return 'L';
 	case TPGS_STATE_OFFLINE:
 		return 'O';
 	case TPGS_STATE_TRANSITIONING:
@@ -542,7 +546,9 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_dh_data *h)
 	int len, k, off, valid_states = 0;
 	char *ucp;
 	unsigned err;
+	unsigned long expiry, interval = 10;
 
+	expiry = round_jiffies_up(jiffies + ALUA_FAILOVER_TIMEOUT);
  retry:
 	err = submit_rtpg(sdev, h);
 
@@ -553,7 +559,7 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_dh_data *h)
 			return SCSI_DH_IO;
 
 		err = alua_check_sense(sdev, &sense_hdr);
-		if (err == ADD_TO_MLQUEUE)
+		if (err == ADD_TO_MLQUEUE && time_before(jiffies, expiry))
 			goto retry;
 		sdev_printk(KERN_INFO, sdev,
 			    "%s: rtpg sense code %02x/%02x/%02x\n",
@@ -587,38 +593,37 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_dh_data *h)
 	}
 
 	sdev_printk(KERN_INFO, sdev,
-		    "%s: port group %02x state %c supports %c%c%c%c%c%c\n",
+		    "%s: port group %02x state %c supports %c%c%c%c%c%c%c\n",
 		    ALUA_DH_NAME, h->group_id, print_alua_state(h->state),
 		    valid_states&TPGS_SUPPORT_TRANSITION?'T':'t',
 		    valid_states&TPGS_SUPPORT_OFFLINE?'O':'o',
+		    valid_states&TPGS_SUPPORT_LBA_DEPENDENT?'L':'l',
 		    valid_states&TPGS_SUPPORT_UNAVAILABLE?'U':'u',
 		    valid_states&TPGS_SUPPORT_STANDBY?'S':'s',
 		    valid_states&TPGS_SUPPORT_NONOPTIMIZED?'N':'n',
 		    valid_states&TPGS_SUPPORT_OPTIMIZED?'A':'a');
 
-	if (h->tpgs & TPGS_MODE_EXPLICIT) {
-		switch (h->state) {
-		case TPGS_STATE_TRANSITIONING:
+	switch (h->state) {
+	case TPGS_STATE_TRANSITIONING:
+		if (time_before(jiffies, expiry)) {
 			/* State transition, retry */
+			interval *= 10;
+			msleep(interval);
 			goto retry;
-			break;
-		case TPGS_STATE_OFFLINE:
-			/* Path is offline, fail */
-			err = SCSI_DH_DEV_OFFLINED;
-			break;
-		default:
-			break;
 		}
-	} else {
-		/* Only Implicit ALUA support */
-		if (h->state == TPGS_STATE_OPTIMIZED ||
-		    h->state == TPGS_STATE_NONOPTIMIZED ||
-		    h->state == TPGS_STATE_STANDBY)
-			/* Useable path if active */
-			err = SCSI_DH_OK;
-		else
-			/* Path unuseable for unavailable/offline */
-			err = SCSI_DH_DEV_OFFLINED;
+		/* Transitioning time exceeded, set port to standby */
+		err = SCSI_DH_RETRY;
+		h->state = TPGS_STATE_STANDBY;
+		break;
+	case TPGS_STATE_OFFLINE:
+	case TPGS_STATE_UNAVAILABLE:
+		/* Path unuseable for unavailable/offline */
+		err = SCSI_DH_DEV_OFFLINED;
+		break;
+	default:
+		/* Useable path if active */
+		err = SCSI_DH_OK;
+		break;
 	}
 	return err;
 }
@@ -672,7 +677,9 @@ static int alua_activate(struct scsi_device *sdev,
 			goto out;
 	}
 
-	if (h->tpgs & TPGS_MODE_EXPLICIT && h->state != TPGS_STATE_OPTIMIZED) {
+	if (h->tpgs & TPGS_MODE_EXPLICIT &&
+	    h->state != TPGS_STATE_OPTIMIZED &&
+	    h->state != TPGS_STATE_LBA_DEPENDENT) {
 		h->callback_fn = fn;
 		h->callback_data = data;
 		err = submit_stpg(h);
@@ -698,8 +705,11 @@ 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 &&
+		 h->state != TPGS_STATE_LBA_DEPENDENT) {
 		ret = BLKPREP_KILL;
 		req->cmd_flags |= REQ_QUIET;
 	}