Commit 10157b1f authored May 14, 2024 by Martin Wilck Committed by Martin K. Petersen May 15, 2024

scsi: core: alua: I/O errors for ALUA state transitions

When a host is configured with a few LUNs and I/O 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 2 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: The original patch was developed by Rajashekhar M A and Hannes
Reinecke. I moved the code 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/



Co-developed-by: Rajashekhar M A <rajs@netapp.com>
Co-developed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin Wilck <martin.wilck@suse.com>
Link: https://lore.kernel.org/r/20240514140344.19538-1-mwilck@suse.com


Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

parent 9f365cb8

drivers/scsi/device_handler/scsi_dh_alua.c

+22 −9

Original line number	Diff line number	Diff line
		@@ -414,28 +414,40 @@ 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 void alua_handle_state_transition(struct scsi_device *sdev)
		{
		struct alua_dh_data *h = sdev->handler_data;
		struct alua_port_group *pg;

		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);
		}

		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
		*/
		alua_handle_state_transition(sdev);
		return NEEDS_RETRY;
		}
		break;
		case UNIT_ATTENTION:
		if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0a) {
		/*
		* LUN Not Accessible - ALUA state transition
		*/
		alua_handle_state_transition(sdev);
		return NEEDS_RETRY;
		}
		if (sense_hdr->asc == 0x29 && sense_hdr->ascq == 0x00) {
		/*
		* Power On, Reset, or Bus Device Reset.
		@@ -502,7 +514,8 @@ static int alua_tur(struct scsi_device *sdev)

		retval = scsi_test_unit_ready(sdev, ALUA_FAILOVER_TIMEOUT * HZ,
		ALUA_FAILOVER_RETRIES, &sense_hdr);
		if (sense_hdr.sense_key == NOT_READY &&
		if ((sense_hdr.sense_key == NOT_READY \|\|
		sense_hdr.sense_key == UNIT_ATTENTION) &&
		sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a)
		return SCSI_DH_RETRY;
		else if (retval)