[PATCH v2 1/4] scsi: scsi_dh_alua: allow I/O in target port unavailable and standby states

[Mauricio Faria de Oliveira]

According to SPC-4 (5.15.2.4.5 Unavailable state), the unavailable
state may (or may not) transition to other states (e.g., microcode
downloading or hardware error, which may be temporary or permanent).

But, scsi_dh_alua currently fails I/O requests early on once that
state occurs (in alua_prep_fn()) preventing path checkers in such
function path to actually check if I/O still fails or now works.

And that prevents a path activation (alua_activate()) which could
update the PG state if it eventually recovered to an active state,
thus resume I/O. (This is also the case with the standby state.)

This might cause device-mapper multipath to fail all paths to some
storage system that moves the controllers to the unavailable state
for firmware upgrades, and never recover regardless of the storage
system doing upgrades one controller at a time and get them online.

Then I/O requests are blocked indefinitely due to queue_if_no_path
but the underlying individual paths are fully operational, and can
be verified as such through other function paths (e.g., SG_IO):

    # multipath -l
    mpatha (360050764008100dac000000000000100) dm-0 IBM,2145
    size=40G features='2 queue_if_no_path retain_attached_hw_handler'
    hwhandler='1 alua' wp=rw
    |-+- policy='service-time 0' prio=0 status=enabled
    | |- 1:0:1:0 sdf 8:80  failed undef running
    | `- 2:0:1:0 sdn 8:208 failed undef running
    `-+- policy='service-time 0' prio=0 status=enabled
      |- 1:0:0:0 sdb 8:16  failed undef running
      `- 2:0:0:0 sdj 8:144 failed undef running

    # strace -e read \
        sg_dd blk_sgio=0 \
        if=/dev/sdj of=/dev/null bs=512 count=1 iflag=direct \
        2>&1 | grep 512
    read(3, 0x3fff7ba80000, 512) = -1 EIO (Input/output error)

    # strace -e ioctl \
        sg_dd blk_sgio=1 \
        if=/dev/sdj of=/dev/null bs=512 count=1 iflag=direct \
        2>&1 | grep 512
    ioctl(3, SG_IO, {'S', SG_DXFER_FROM_DEV, cmd[10]=[28, 00, 00, 00,
    00, 00, 00, 00, 01, 00], <...>) = 0

So, allow I/O to paths of PGs in unavailable/standby state, so path
checkers can actually check them.

Also, schedule a recheck when unavailable/standby state is detected
(in alua_check_sense()) to update pg->state, and quiet further SCSI
error messages (in alua_prep_fn()).

Once a path checker eventually detects a working/active state again,
the PG state is normally updated on path activation (alua_activate(),
as it schedules a recheck), thus I/O requests are no longer failed.

Signed-off-by: Mauricio Faria de Oliveira <mauricfo@xxxxxxxxxxxxxxxxxx>
Reported-by: Naresh Bannoth <nbannoth@xxxxxxxxxx>

---
v2:
- also add support for standby state to alua_check_sense(), alua_prep_fn()
  (Bart Van Assche <Bart.VanAssche@xxxxxxxxxxx>)

 drivers/scsi/device_handler/scsi_dh_alua.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index c01b47e5b55a..a1cf3d6aa853 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -431,6 +431,26 @@ static int alua_check_sense(struct scsi_device *sdev,
 			alua_check(sdev, false);
 			return NEEDS_RETRY;
 		}
+		if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0b) {
+			/*
+			 * LUN Not Accessible - target port in standby state.
+			 *
+			 * Do not retry, so failover to another target port occur.
+			 * Schedule a recheck to update state for other functions.
+			 */
+			alua_check(sdev, true);
+			return SUCCESS;
+		}
+		if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0c) {
+			/*
+			 * LUN Not Accessible - target port in unavailable state.
+			 *
+			 * Do not retry, so failover to another target port occur.
+			 * Schedule a recheck to update state for other functions.
+			 */
+			alua_check(sdev, true);
+			return SUCCESS;
+		}
 		break;
 	case UNIT_ATTENTION:
 		if (sense_hdr->asc == 0x29 && sense_hdr->ascq == 0x00) {
@@ -1057,6 +1077,8 @@ static void alua_check(struct scsi_device *sdev, bool force)
  *
  * Fail I/O to all paths not in state
  * active/optimized or active/non-optimized.
+ * Allow I/O to paths in state unavailable/standby
+ * so path checkers can actually check them.
  */
 static int alua_prep_fn(struct scsi_device *sdev, struct request *req)
 {
@@ -1072,6 +1094,9 @@ static int alua_prep_fn(struct scsi_device *sdev, struct request *req)
 	rcu_read_unlock();
 	if (state == SCSI_ACCESS_STATE_TRANSITIONING)
 		ret = BLKPREP_DEFER;
+	else if (state == SCSI_ACCESS_STATE_UNAVAILABLE ||
+		 state == SCSI_ACCESS_STATE_STANDBY)
+		req->rq_flags |= RQF_QUIET;
 	else if (state != SCSI_ACCESS_STATE_OPTIMAL &&
 		 state != SCSI_ACCESS_STATE_ACTIVE &&
 		 state != SCSI_ACCESS_STATE_LBA) {
-- 
1.8.3.1