Re: [PATCH 00/16] scsi: libsas and users: Factor out LLDD TMF code

[John Garry]

On 03/02/2022 09:44, Damien Le Moal wrote:

Hi Damien,

> > > > [  385.102073] sas: Enter sas_scsi_recover_host busy: 1 failed: 1
> > > > [  385.108026] sas: sas_scsi_find_task: aborting task 0x000000007068ed73
> > > > [  405.561099] pm80xx0:: pm8001_exec_internal_task_abort  757:TMF task

Contrary to mentioning TMF in the log, this is not a TMF but rather an 
internal abort timing out. I don't think that this should ever happen. 
This command should just abort pending IO commands in the controller and 
not send anything to the target. So for this to timeout means a HW fault 
or driver bug. And I did not touch this code for pm8001.

> > > > timeout.
> > > > [  405.568236] sas: sas_scsi_find_task: task 0x000000007068ed73 is
> > > > aborted
> > > > [  405.574930] sas: sas_eh_handle_sas_errors: task 0x000000007068ed73 is
> > > > aborted
> > > > [  411.192602] ata21.00: qc timeout (cmd 0xec)
> > > > [  431.672122] pm80xx0:: pm8001_exec_internal_task_abort  757:TMF task
> > > > timeout.
> > > > [  431.679282] ata21.00: failed to IDENTIFY (I/O error, err_mask=0x4)
> > > > [  431.685544] ata21.00: revalidation failed (errno=-5)
> > > > [  441.911948] ata21.00: qc timeout (cmd 0xec)
> > > > [  462.391545] pm80xx0:: pm8001_exec_internal_task_abort  757:TMF task
> > > > timeout.
> > > > [  462.398696] ata21.00: failed to IDENTIFY (I/O error, err_mask=0x4)
> > > > [  462.404992] ata21.00: revalidation failed (errno=-5)
> > > > [  492.598769] ata21.00: qc timeout (cmd 0xec)
> > > > ...

Do you have a fuller dmesg with my series?

...

> > }
> > - res = -TMF_RESP_FUNC_FAILED;
> > + res = TMF_RESP_FUNC_FAILED;
> >
> > That's effectively the same as what I have in this series in
> > sas_execute_tmf().
> >
> > However your testing is a SATA device, which I'll check further.
> This did not help. Still seeing 100% reproducible hangs.

OK, but I think that we should also have this change as the mainline 
codes looks broken to be begin with:

--->8 ---

[PATCH] scsi: libsas: Handle all errors in sas_scsi_find_task()

LLDD TMFs callbacks may return linux or other error codes instead of TMF
codes. This may cause problems in sas_scsi_find_task() ->
.lldd_query_task(), as only TMF codes are handled there. As such, we may
not return a task_disposition type. Function sas_eh_handle_sas_errors() 
only handles that type, and may exit error
handling early for unrecognised types.

So use TASK_ABORT_FAILED for non-TMF types returned from
.lldd_query_task(), on the assumption that the command may still be 
alive and error handling should be escalated.

Signed-off-by: John Garry <john.garry@xxxxxxxxxx>

diff --git a/drivers/scsi/libsas/sas_scsi_host.c 
b/drivers/scsi/libsas/sas_scsi_host.c
index 53d8b7ede0cd..02274f471308 100644
--- a/drivers/scsi/libsas/sas_scsi_host.c
+++ b/drivers/scsi/libsas/sas_scsi_host.c
@@ -316,8 +316,11 @@ static enum task_disposition 
sas_scsi_find_task(struct sas_task *task)
 				pr_notice("%s: task 0x%p failed to abort\n",
 					  __func__, task);
 				return TASK_ABORT_FAILED;
+			default:
+				pr_notice("%s: task 0x%p result code %d not handled, assuming 
failed\n",
+					  __func__, task, res);
+				return TASK_ABORT_FAILED;
 			}
-
 		}
 	}
 	return res;

---8< ----

> I did a lot of testing/digging today, 

Thanks for the effort!

> and the hang cause seems to be
> missing task completions.
> At random, a task times out as its completion

That sounds fimilar to my general issue running this driver on an arm64 
host...

> does not come, and subsequent abort trial for the task fail, revalidate
> fails

I assume SMP IOs fail if revalidation fails - if this is the case, then 
the controller seems to be in bad state.

> and the device is dropped (capacity goes to 0). But at that point,
> doing rmmod/modprobe to reset the device does not work. sync cache
> command issued at rmmod time never completes. I end up needing to power
> cycle the machine every time...
>
> No clue about the root cause yet, but it definitely seem to be related
> to NCQ/high QD operation. If I force my tests to use non-NCQ commands,
> everything is fine and the tests run to completion without any issue.
>
> I wonder if their is a tag management bug somewhere...

Maybe. Not sure.

On a related point, Hannes' change here could avoid it:

https://lore.kernel.org/linux-scsi/20210222132405.91369-32-hare@xxxxxxx/

> I did stumble on something very ugly in libsas too: sas_ata_qc_issue()
> drops and retake the ata port lock. No other ATA driver do that since
> the ata completion also take that lock. The ata port lock is taken
> before ata_qc_issue() is called with IRQ disabled (spin_lock_irqsave()).
> So doing a spin_unlock()/spin_lock() in sas_ata_qc_issue() (called from
> ata_qc_issue()) seems like a very bad idea. I removed that and
> everything work the same way (the lld execute does not sleep). But that
> did not solve the hang problem.

I would need to check why this is done again. Before my time...

> Of note is this is all with your libsas patches applied. Without the
> patches, I have KASAN screaming at me about use-after-free in completion
> context. With your patches, KASAN is silent.
>
> Another thing: this driver does not allow changing the max qd... Very
> annoying.
>
> echo 1 > /sys/block/sdX/device/queue_depth
>
> has no effect. QD stays at 32 for an ATA drive. Need to look into that too.

I had a look at this. It seems that we fail in 
__ata_change_queue_depth() -> ata_scsi_find_dev() returning NULL.

Thanks again for your effort, I will continue to look.

john