Re: [PATCH] ata: libata-scsi: fix bogus SCSI sense after abort

From: Lorenz Brun
Date: Thu Jun 29 2023 - 15:18:34 EST


Am Mo, 26. Jun 2023 um 16:51:47 +09:00:00 schrieb Damien Le Moal <dlemoal@xxxxxxxxxx>:
On 6/26/23 16:46, Hannes Reinecke wrote:
On 6/26/23 09:29, Damien Le Moal wrote:
On 6/24/23 03:19, Lorenz Brun wrote:
Since commit 058e55e120ca which fixed that commands without valid
error/status codes did not result in any sense error, the returned sense
errors were completely bogus as ata_to_sense_error did not have valid
inputs in the first place.

For example the following ATA error

exception Emask 0x10 SAct 0x20c000 SErr 0x280100 action 0x6 frozen
irq_stat 0x08000000, interface fatal error
SError: { UnrecovData 10B8B BadCRC }
failed command: READ FPDMA QUEUED
cmd 60/e0:70:20:0a:00/00:00:00:00:00/40 tag 14 ncq dma 114688 in
res 40/00:ac:20:5e:50/00:00:5d:01:00/40 Emask 0x10 (ATA bus error)
status: { DRDY }

got turned into the following nonsensical SCSI error

FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
Sense Key : Illegal Request [current]
Add. Sense: Unaligned write command
CDB: Read(16) 88 00 00 00 00 00 00 00 0a 20 00 00 00 e0 00 00

This has nothing to do with an unaligned write command, but is due to an
ATA EH-triggered abort. But ata_to_sense_error only knows about
status and error, both of which aren't even valid here as the command
has been aborted.

Add an additional section to ata_gen_ata_sense which handles
errors not coming from the device first, before calling into
ata_to_sense_error.

According to the SAT-5 spec a reset should cause a Unit Attention event,
which the SCSI subsystem should handle to retry its commands but I
am not sure how much of that infra is present in Linux's SCSI layer, so
this is a simpler solution.

Signed-off-by: Lorenz Brun <lorenz@xxxxxxxx>
---
drivers/ata/libata-scsi.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 551077cea4e4..61c6a4e8123a 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -13,6 +13,7 @@
* - http://www.t13.org/
*/

+#include "scsi/scsi_proto.h"
#include <linux/compat.h>
#include <linux/slab.h>
#include <linux/kernel.h>
@@ -1013,6 +1014,21 @@ static void ata_gen_ata_sense(struct ata_queued_cmd *qc)
ata_scsi_set_sense(dev, cmd, NOT_READY, 0x04, 0x21);
return;
}
+ if (qc->err_mask & (AC_ERR_HSM | AC_ERR_ATA_BUS | AC_ERR_HOST_BUS |
+ AC_ERR_SYSTEM | AC_ERR_OTHER)) {

Did you check SATA IO specs and/or AHCI to see if that says anything about these
? And I wonder if we should check if we have something in tf->status and
tf->error...

We really should. The above combination of error masks seems pretty
arbitrary, as actually you do _not_ want to check for there error mask,
but rather for the fact that the sense code is bogus.
So shouldn't we rather test for that one directly?
SCISI / ATA Translation (SAT)-5 has the following to say about it:

A SATL that detects a link reset sequence for a Serial ATA device or initiates any reset of an ATA device shall
establish a unit attention condition on behalf of the emulated logical unit corresponding to the ATA device with
the sense key set to UNIT ATTENTION and the additional sense code set to POWER ON, RESET, OR BUS
DEVICE RESET OCCURRED for the SCSI initiator port associated with each I_T nexus. The method a SATL
uses to detect a link reset sequence on the SATA link is vendor specific.

I am however not sufficiently familiar with SCSI and especially the SCSI midlayer in Linux to know how this Unit Attention causes the requests to be aborted.

As a simpler fix I checked which err_maks cause a reset and in that case report this error. I'd be happier with the proper SAT-5 solution, but it looks like it would be quite a significant change.


+ /* Command aborted because of some issue with the ATA subsystem
+ * Should technically cause unit attention, but this is better
+ * than nothing, which results in nonsensical errors.
+ * POWER ON, RESET, OR BUS DEVICE RESET OCCURRED
+ */

Multi-line comment style: start with a "/*" line please. The phrasing of the
comment is not very clear. Maybe something like:

/*
* If the command aborted because of some issue with the
* adapter or link, report a POWER ON, RESET, OR BUS DEVICE
* RESET OCCURRED error.
*/

Did you check that all of the above error flags lead to a drive reset ? The
issue I have with this is that the drive reset is triggered by libata EH after
it got these bad errors but the sense data you use here normally indicate that
the reset was initiated by the adapter or the drive. Not sure this is ideal.

Yes. We should rather return a DID_RESET status instead of any made up
sense code for which we don't have a good justification, and which might
get invalidated by future SATL versions.

Need to check what SAT says about all this as well... Will do some spec reading.
The default sense code for when we cannot figure out proper sense based on
status and error is ABORTED COMMAND/0/0. That seems good enough to me. The issue
may be that we do not reach that default case when we have bogus status/error.
The test:

if (qc->err_mask ||
tf->status & (ATA_BUSY | ATA_DF | ATA_ERR | ATA_DRQ)) {

in ata_gen_ata_sense() is sketchy... Why is that qc->err_mask there ? It does
not seem needed at all. If removed, then we would fall back to aborted command
default.
From reading SAT-5 I think most of this function is bogus, but I don't know enough about the pieces involved to come up with the "correct" fix.

Regards,
Lorenz