[PATCH v2] I/O errors for ALUA state transitions

Martin Wilck
2024-05-03T19:56:18Z

When a host is configured with a few LUNs and IO is running,
injecting FC faults repeatedly leads to path recovery problems.
The LUNs have 4 paths each and 3 of them come back active after
say an FC fault which makes two of the paths go down, instead of
all 4. This happens after several iterations of continuous FC faults.

Reason here is that we're returning an I/O error whenever we're
encountering sense code 06/04/0a (LOGICAL UNIT NOT ACCESSIBLE,
ASYMMETRIC ACCESS STATE TRANSITION) instead of retrying.

mwilck: Resending a modified version of this patch, which was originally
authored by Rajashekhar M A from Netapp, and submitted in 2021.
Moved the changes to alua_check_sense() as suggested by Mike Christie [1].
Evan Milne had raised the question whether pg->state should be set to
transitioning in the UA case [2]. I believe that doing this is
correct. SCSI_ACCESS_STATE_TRANSITIONING by itself doesn't cause I/O
errors. Our handler schedules an RTPG, which will only result in an I/O
error condition if the transitioning timeout expires.

[1] https://lore.kernel.org/all/0bc96e82-fdda-4187-148d-5b34f81d4942@oracle.com/
[2] https://lore.kernel.org/all/CAGtn9r=kicnTDE2o7Gt5Y=yoidHYD7tG8XdMHEBJTBraVEoOCw@mail.gmail.com/

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin Wilck <mwilck@suse.com>
Co-authored-by: Rajashekhar M A <rajs@netapp.com>
---
drivers/scsi/device_handler/scsi_dh_alua.c | 34 +++++++++++++---------
1 file changed, 20 insertions(+), 14 deletions(-)

diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index a226dc1b65d7..682d5bb53d14 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -414,28 +414,34 @@ static char print_alua_state(unsigned char state)
}
}

-static enum scsi_disposition alua_check_sense(struct scsi_device *sdev,
- struct scsi_sense_hdr *sense_hdr)
+static enum scsi_disposition alua_handle_state_transition(struct scsi_device *sdev)
{
struct alua_dh_data *h = sdev->handler_data;
struct alua_port_group *pg;

+ /*
+ * LUN Not Accessible - ALUA state transition
+ */
+ rcu_read_lock();
+ pg = rcu_dereference(h->pg);
+ if (pg)
+ pg->state = SCSI_ACCESS_STATE_TRANSITIONING;
+ rcu_read_unlock();
+ alua_check(sdev, false);
+ return NEEDS_RETRY;
+}
+
+static enum scsi_disposition alua_check_sense(struct scsi_device *sdev,
+ struct scsi_sense_hdr *sense_hdr)
+{
switch (sense_hdr->sense_key) {
case NOT_READY:
- if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0a) {
- /*
- * LUN Not Accessible - ALUA state transition
- */
- rcu_read_lock();
- pg = rcu_dereference(h->pg);
- if (pg)
- pg->state = SCSI_ACCESS_STATE_TRANSITIONING;
- rcu_read_unlock();
- alua_check(sdev, false);
- return NEEDS_RETRY;
- }
+ if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0a)
+ return alua_handle_state_transition(sdev);
break;
case UNIT_ATTENTION:
+ if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0a)
+ return alua_handle_state_transition(sdev);
if (sense_hdr->asc == 0x29 && sense_hdr->ascq == 0x00) {
/*
* Power On, Reset, or Bus Device Reset.
--
2.44.0