On Mon, 2017-04-10 at 22:17 -0300, 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
> conditions, respectively).
>
> But, scsi_dh_alua currently fails the I/O requests early once that
> state is established (in alua_prep_fn()), which provides no chance
> for path checkers going through that function path to really check
> whether the path actually still fails I/O requests or recovered to
> an active 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 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 if=/dev/sdj of=/dev/null bs=512 count=1 iflag=direct \
> blk_sgio=1 \
> 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 target port (groups) in the unavailable state, so the
> path checkers can actually check them, and schedule a recheck whenever
> the unavailable state is detected so pg->state can be updated properly
> (and further SCSI IO error messages then silenced through alua_prep_fn()).
>
> Once a path checker eventually detects an active state again, the port
> group state will be updated by the path activation call, alua_activate(),
> as it schedules an alua_rtpg() check.
>
> Signed-off-by: Mauricio Faria de Oliveira <mauri...@linux.vnet.ibm.com>
> Reported-by: Naresh Bannoth <nbann...@in.ibm.com>
> ---
> drivers/scsi/device_handler/scsi_dh_alua.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c
> b/drivers/scsi/device_handler/scsi_dh_alua.c
> index c01b47e5b55a..5e5a33cac951 100644
> --- a/drivers/scsi/device_handler/scsi_dh_alua.c
> +++ b/drivers/scsi/device_handler/scsi_dh_alua.c
> @@ -431,6 +431,20 @@ static int alua_check_sense(struct scsi_device *sdev,
> alua_check(sdev, false);
> return NEEDS_RETRY;
> }
> + if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0c) {
> + /*
> + * LUN Not Accessible - target port in unavailable
> state.
> + *
> + * It may (not) be possible to transition to other
> states;
> + * the transition might take a while or not happen at
> all,
> + * depending on the storage system model, error type,
> etc.
> + *
> + * 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 +1071,8 @@ 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 all paths in state unavailable
> + * so path checkers can actually check them.
> */
> static int alua_prep_fn(struct scsi_device *sdev, struct request *req)
> {
> @@ -1072,6 +1088,8 @@ 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)
> + req->rq_flags |= RQF_QUIET;
> else if (state != SCSI_ACCESS_STATE_OPTIMAL &&
> state != SCSI_ACCESS_STATE_ACTIVE &&
> state != SCSI_ACCESS_STATE_LBA) {
Hello Mauricio,
Please also add support for the "standby" state to both alua_check_sense()
and alua_prep_fn() while you are modifying these functions.
Thanks,
Bart.
