On 10/7/19 10:45 PM, Ewan D. Milne wrote: > See below. > > On Mon, 2019-10-07 at 15:57 +0200, Hannes Reinecke wrote: >> From: Hannes Reinecke <[email protected]> >> >> Some arrays are not capable of returning RTPG data during state >> transitioning, but rather return an 'LUN not accessible, asymmetric >> access state transition' sense code. In these cases we >> can set the state to 'transitioning' directly and don't need to >> evaluate the RTPG data (which we won't have anyway). >> >> Signed-off-by: Hannes Reinecke <[email protected]> >> --- >> drivers/scsi/device_handler/scsi_dh_alua.c | 21 ++++++++++++++++----- >> 1 file changed, 16 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c >> b/drivers/scsi/device_handler/scsi_dh_alua.c >> index 4971104b1817..f32da0ca529e 100644 >> --- a/drivers/scsi/device_handler/scsi_dh_alua.c >> +++ b/drivers/scsi/device_handler/scsi_dh_alua.c >> @@ -512,6 +512,7 @@ static int alua_rtpg(struct scsi_device *sdev, struct >> alua_port_group *pg) >> unsigned int tpg_desc_tbl_off; >> unsigned char orig_transition_tmo; >> unsigned long flags; >> + bool transitioning_sense = false; >> >> if (!pg->expiry) { >> unsigned long transition_tmo = ALUA_FAILOVER_TIMEOUT * HZ; >> @@ -572,13 +573,19 @@ static int alua_rtpg(struct scsi_device *sdev, struct >> alua_port_group *pg) >> goto retry; >> } >> /* >> - * Retry on ALUA state transition or if any >> - * UNIT ATTENTION occurred. >> + * If the array returns with 'ALUA state transition' >> + * sense code here it cannot return RTPG data during >> + * transition. So set the state to 'transitioning' directly. >> */ >> if (sense_hdr.sense_key == NOT_READY && >> - sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a) >> - err = SCSI_DH_RETRY; >> - else if (sense_hdr.sense_key == UNIT_ATTENTION) >> + sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a) { >> + transitioning_sense = true; >> + goto skip_rtpg; >> + } >> + /* >> + * Retry on any other UNIT ATTENTION occurred. >> + */ >> + if (sense_hdr.sense_key == UNIT_ATTENTION) >> err = SCSI_DH_RETRY; >> if (err == SCSI_DH_RETRY && >> pg->expiry != 0 && time_before(jiffies, pg->expiry)) { >> @@ -666,7 +673,11 @@ static int alua_rtpg(struct scsi_device *sdev, struct >> alua_port_group *pg) >> off = 8 + (desc[7] * 4); >> } >> >> + skip_rtpg: >> spin_lock_irqsave(&pg->lock, flags); >> + if (transitioning_sense) >> + pg->state = SCSI_ACCESS_STATE_TRANSITIONING; >> + >> sdev_printk(KERN_INFO, sdev, >> "%s: port group %02x state %c %s supports %c%c%c%c%c%c%c\n", >> ALUA_DH_NAME, pg->group_id, print_alua_state(pg->state), > > The patch itself looks OK, but I was wondering about a couple of things: > > - There are other places in scsi_dh_alua where the ASC/ASCQ 04 0A is checked > and we retry, I understand that this is a particular case you are solving > but is the changing of the state to -> transitioning (because that's what > the device said the state was) applicable in those other cases? No. The original code was built around the assumption that RTPG would return the status of the device; consequently we would have to retry RTPG until we get a final status. But as mentioned, there are arrays which cannot return RTPG data during transitioning, so the code would never be able to detect a transitioning state. With this patch we set the state directly once the said sense code is received. But this applies _only_ to the RTPG command, as this is required to move the state machine along. None of the other commands are affected.
> - The code originally seems to have been under the assumption that the > transitioning state was a transient event, so the retry would pick up > the eventual state. Now, some storage arrays spend a long time in the > transitioning state, but if we don't send another command are we going to > get the sense (or the UA) that triggers entry to the eventual ALUA state? > Note, there are two types of retries. The one is the 'normal' command retry, where we resend a command a given number of times to retrieve the final status. This is precisely the error which caused this patch. And then there is a scheduled retry; here we essentially poll the array with sending RTPG in regular intervals until the 'transitioning' state is gone. (Check for 'alua_rtpg()' and the handling of the SCSI_DH_RETRY return value). With the patch we continue to trigger that second type of retries, which will eventually clear the transitioning state. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking [email protected] +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 247165 (AG München), GF: Felix Imendörffer
