On 03/02/2017 09:16 PM, Benjamin Block wrote:
> Hej Hannes,
>
> On Wed, Mar 01, 2017 at 10:15:15AM +0100, Hannes Reinecke wrote:
>> The current medium access timeout counter will be increased for
>> each command, so if there are enough failed commands we'll hit
>> the medium access timeout for even a single failure.
>> Fix this by making the timeout per EH run, ie the counter will
>> only be increased once per device and EH run.
>>
>> Cc: Ewan Milne <emi...@redhat.com>
>> Cc: Lawrence Obermann <lober...@redhat.com>
>> Cc: Benjamin Block <bbl...@linux.vnet.ibm.com>
>> Cc: Steffen Maier <ma...@de.ibm.com>
>> Signed-off-by: Hannes Reinecke <h...@suse.com>
>
> Steffen already suggested it, It would be nice to have a stable-tag
> here. This already caused multiple real-world false-positive outages, I
> think that qualifies for stable :)
>
>> ---
>> drivers/scsi/scsi_error.c | 16 +++++++++++++++-
>> drivers/scsi/sd.c | 21 +++++++++++++++++----
>> drivers/scsi/sd.h | 1 +
>> include/scsi/scsi_driver.h | 2 +-
>> 4 files changed, 34 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
>> index f2cafae..cec439c 100644
>> --- a/drivers/scsi/scsi_error.c
>> +++ b/drivers/scsi/scsi_error.c
>> @@ -58,6 +58,7 @@
>> static int scsi_eh_try_stu(struct scsi_cmnd *scmd);
>> static int scsi_try_to_abort_cmd(struct scsi_host_template *,
>> struct scsi_cmnd *);
>> +static int scsi_eh_reset(struct scsi_cmnd *scmd);
>>
>> /* called with shost->host_lock held */
>> void scsi_eh_wakeup(struct Scsi_Host *shost)
>> @@ -249,6 +250,7 @@ int scsi_eh_scmd_add(struct scsi_cmnd *scmd, int eh_flag)
>> if (scmd->eh_eflags & SCSI_EH_ABORT_SCHEDULED)
>> eh_flag &= ~SCSI_EH_CANCEL_CMD;
>> scmd->eh_eflags |= eh_flag;
>> + scsi_eh_reset(scmd);
>> list_add_tail(&scmd->eh_entry, &shost->eh_cmd_q);
>> shost->host_failed++;
>> scsi_eh_wakeup(shost);
>> @@ -1107,7 +1109,19 @@ static int scsi_eh_action(struct scsi_cmnd *scmd, int
>> rtn)
>> if (!blk_rq_is_passthrough(scmd->request)) {
>> struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);
>> if (sdrv->eh_action)
>> - rtn = sdrv->eh_action(scmd, rtn);
>> + rtn = sdrv->eh_action(scmd, rtn, false);
>> + }
>> + return rtn;
>> +}
>> +
>> +static int scsi_eh_reset(struct scsi_cmnd *scmd)
>> +{
>> + int rtn = SUCCESS;
>> +
>> + if (!blk_rq_is_passthrough(scmd->request)) {
>> + struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);
>> + if (sdrv->eh_action)
>> + rtn = sdrv->eh_action(scmd, rtn, true);
>> }
>> return rtn;
>> }
>> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
>> index c7839f6..c794686 100644
>> --- a/drivers/scsi/sd.c
>> +++ b/drivers/scsi/sd.c
>> @@ -115,7 +115,7 @@
>> static int sd_init_command(struct scsi_cmnd *SCpnt);
>> static void sd_uninit_command(struct scsi_cmnd *SCpnt);
>> static int sd_done(struct scsi_cmnd *);
>> -static int sd_eh_action(struct scsi_cmnd *, int);
>> +static int sd_eh_action(struct scsi_cmnd *, int, bool);
>> static void sd_read_capacity(struct scsi_disk *sdkp, unsigned char *buffer);
>> static void scsi_disk_release(struct device *cdev);
>> static void sd_print_sense_hdr(struct scsi_disk *, struct scsi_sense_hdr *);
>> @@ -1689,18 +1689,28 @@ static int sd_pr_clear(struct block_device *bdev,
>> u64 key)
>> * sd_eh_action - error handling callback
>> * @scmd: sd-issued command that has failed
>> * @eh_disp: The recovery disposition suggested by the midlayer
>> + * @reset: Reset medium access counter
>> *
>> * This function is called by the SCSI midlayer upon completion of an
>> * error test command (currently TEST UNIT READY). The result of sending
>> * the eh command is passed in eh_disp. We're looking for devices that
>> * fail medium access commands but are OK with non access commands like
>> * test unit ready (so wrongly see the device as having a successful
>> - * recovery)
>> + * recovery).
>> + * We have to be careful to count a medium access failure only once
>> + * per SCSI EH run; there might be several timed out commands which
>> + * will cause the 'max_medium_access_timeouts' counter to trigger
>> + * after the first SCSI EH run already and set the device to offline.
>> **/
>> -static int sd_eh_action(struct scsi_cmnd *scmd, int eh_disp)
>> +static int sd_eh_action(struct scsi_cmnd *scmd, int eh_disp, bool reset)
>> {
>> struct scsi_disk *sdkp = scsi_disk(scmd->request->rq_disk);
>>
>> + if (reset) {
>> + /* New SCSI EH run, reset gate variable */
>> + sdkp->medium_access_reset = 0;
>> + return eh_disp;
>> + }
>> if (!scsi_device_online(scmd->device) ||
>> !scsi_medium_access_command(scmd) ||
>> host_byte(scmd->result) != DID_TIME_OUT ||
>> @@ -1714,7 +1724,10 @@ static int sd_eh_action(struct scsi_cmnd *scmd, int
>> eh_disp)
>> * process of recovering or has it suffered an internal failure
>> * that prevents access to the storage medium.
>> */
>> - sdkp->medium_access_timed_out++;
>> + if (!sdkp->medium_access_reset) {
>> + sdkp->medium_access_timed_out++;
>> + sdkp->medium_access_reset = 1;
>> + }
>>
>> /*
>> * If the device keeps failing read/write commands but TEST UNIT
>> diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
>> index 4dac35e..6a4f75a 100644
>> --- a/drivers/scsi/sd.h
>> +++ b/drivers/scsi/sd.h
>> @@ -106,6 +106,7 @@ struct scsi_disk {
>> unsigned rc_basis: 2;
>> unsigned zoned: 2;
>> unsigned urswrz : 1;
>> + unsigned medium_access_reset : 1;
>> };
>> #define to_scsi_disk(obj) container_of(obj,struct scsi_disk,dev)
>>
>> diff --git a/include/scsi/scsi_driver.h b/include/scsi/scsi_driver.h
>> index 891a658..d5e0012 100644
>> --- a/include/scsi/scsi_driver.h
>> +++ b/include/scsi/scsi_driver.h
>> @@ -15,7 +15,7 @@ struct scsi_driver {
>> int (*init_command)(struct scsi_cmnd *);
>> void (*uninit_command)(struct scsi_cmnd *);
>> int (*done)(struct scsi_cmnd *);
>> - int (*eh_action)(struct scsi_cmnd *, int);
>> + int (*eh_action)(struct scsi_cmnd *, int, bool);
>> };
>> #define to_scsi_driver(drv) \
>> container_of((drv), struct scsi_driver, gendrv)
>> --
>> 1.8.5.6
>>
>
> Bart already made some suggestions that I think are good, otherwise I
> have nothing big to add. Should work just fine.
>
> The only thing that still bugs me about this is the corner-case we
> talked about the last time we talked about this. No show-stopper for me,
> but I though I might as well mention it.
>
> When we do the different escalation-stages in scsi_unjam_host(), we
> always have the same basic pattern:
>
> for_all_in(work_q)) {
> cmd = get_next(eh_work_q);
>
> do_action(cmd); /* might be abort, lun_reset, target_reset, ... */
>
> if (was_ok()) {
> move_to(check_list, cmd);
> move_same_scope_to(check_list, work_q);
> }
> }
>
> for_all_in(check_list) {
> cmd = get_next(eh_work_q);
> sdev = get_sdev(cmd);
>
> test_device(sdev); /* TUR and maybe STU */
>
> for_all_in_same_scope_in(check_list) {
> if (test_was_ok() && scsi_eh_action(scmd, SUCCESS) == SUCCESS)
> move_to(done_q, cmd)
> else
> move_to(work_q, cmd)
> }
> }
>
> return list_empty(eh_work_q)
>
> (I hope I have this right, irritatingly this 'looks' different for no
> reason I can see for the different stages).
>
> The corner-case being, if we have a cmd that failes in scsi_eh_action(),
> it will be put back into the work_q. But all other command for the same
> scope will be put into the done_q because for them, sd_eh_action()
> will early-return with SUCCESS (sdev is not online anymore).
>
> Then, because the work_q is not empty, we will escalate to the next
> step. Worst case being, we escalate to host_reset, although EH is
> actually already done - we already decided that this sdev is offline in
> SD and even when we go through host-reset it will not become running
> anymore.. which makes the whole host-reset a big waste of time.
>
> AFAIK the escalate to Host-Reset can only happen if the LLD has no
> pointer for STU, LUN-, Target- and Bus-Reset, so its actually not as
> bad, but I still think its something we should correct.
>
> If you don't wanna change this here, I can probably send a part of the
> patch I made for this some time ago.
>
Hmm. Shouldn't this resolved by simply returning 'SUCCESS' in
sd_eh_action() when it decides to take the device offline?
IE doing something like this:
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index c794686..311ac3c 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1739,7 +1739,7 @@ static int sd_eh_action(struct scsi_cmnd *scmd,
int eh_dis
p, bool reset)
"Medium access timeout failure. Offlining
disk!\n");
scsi_device_set_state(scmd->device, SDEV_OFFLINE);
- return FAILED;
+ return SUCCESS;
}
return eh_disp;
would help, no?
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
h...@suse.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)
