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Message-ID: <b6e97d03-0e1b-df2a-70e2-3247833f3aac@suse.de>
Date: Tue, 11 Jul 2017 11:18:28 +0200
From: Hannes Reinecke <hare@...e.de>
To: Mauricio Faria de Oliveira <mauricfo@...ux.vnet.ibm.com>,
jejb@...ux.vnet.ibm.com, martin.petersen@...cle.com
Cc: bart.vanassche@...disk.com, linux-scsi@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] scsi: scsi_dh_alua: allow I/O in target port
unavailable and standby states
On 07/11/2017 12:47 AM, Mauricio Faria de Oliveira wrote:
> 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@...ux.vnet.ibm.com>
> Reported-by: Naresh Bannoth <nbannoth@...ibm.com>
>
> ---
> v2:
> - also add support for standby state to alua_check_sense(), alua_prep_fn()
> (Bart Van Assche <Bart.VanAssche@...disk.com>)
>
> 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) {
>
NACK.
The whole _point_ of having device handlers is to _avoid_ I/O errors
during booting.
And the ALUA checker is prepared to handle this situation properly.
The directio checker of course doesn't know about this, but then no-one
expected the directio checker to work with ALUA.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@...e.de +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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