Re: [PATCH v5 0/7] libsas and drivers: NCQ error handling

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 10/6/22 23:45, Niklas Cassel wrote:
> On Thu, Oct 06, 2022 at 09:33:23AM +0100, John Garry wrote:
>> On 05/10/2022 23:42, Damien Le Moal wrote:
>>>> Hello Damien,
>>>>
>>>> John explained that he got a timeout from EH when reading the log:
>>>> [  350.281581] ata1: failed to read log page 10h (errno=-5)
>>>> [  350.577181] ata1.00: exception Emask 0x1 SAct 0xffffffff SErr 0x0 action 0x6 frozen
>>>>
>>>> ata_eh_read_log_10h() uses ata_read_log_page(), which will first try to read
>>>> the log using READ LOG DMA EXT. If that fails, it will retry using READ LOG EXT.
>>>>
>>>> Therefore, to see if this is a driver specific bug, I suggested to try to read
>>>> the NCQ Command Error log using ATA16 passthrough commands:
>>>>
>>>> $ sudo sg_sat_read_gplog -d --log=0x10 /dev/sdc
>>>> will read the log using READ LOG DMA EXT.
>>>>
>>>> $ sudo sg_sat_read_gplog --log=0x10 /dev/sdc
>>>> will read the log using READ LOG EXT.
>>
>> Note that I can't get a distro to boot on this system from the HDD for the
>> same timeout problem (so no tools easily available).
>>
>>>>
>>>> Neither of these two suggested commands are NCQ commands.
>>>> (Neither command is encapsulated in a RECEIVE FPDMA QUEUED,
>>>> so I'm not sure what you mean.)
>>>>
>>>>
>>>> Garry, I now see that:
>>>> [  350.577181] ata1.00: exception Emask 0x1 SAct 0xffffffff SErr 0x0 action 0x6 frozen
>>>> Your port is frozen.
>>>>
>>>> ata_read_log_page() calls ata_exec_internal() which calls ata_exec_internal_sg(),
>>>> which will simply return an error without sending down the command to the drive,
>>>> if the port is frozen.
>>>>
>>>> Not sure why your port is frozen, mine is obviously not.
>>
>> I think that it gets frozen when the internal command for read log ext times
>> out. More below about that timeout.
> 
> ata_read_log_page() will first try to read using READ LOG DMA EXT.
> If that fails it will retry with READ LOG EXT.
> 
> Your log has this:
> [  350.257870] ata1.00: qc timeout (cmd 0x47)
> 
> So it is definitely ATA_CMD_READ_LOG_DMA_EXT that times out.
> 
> On timeout, ata_exec_internal_sg() will freeze the port:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/ata/libata-core.c?h=v6.0#n1577
> 
> When ata_read_log_page() retries with the port frozen,
> READ LOG EXT will obviously fail (since the port is frozen).
> 
> Not sure why READ LOG DMA EXT would timeout for you...
> Perhaps your drive does not implement this command,
> and incorrectly reports supporting this command via
> ata_id_has_read_log_dma_ext().
> 
> Perhaps you could try boot your kernel with libata.force=nodmalog
> on the kernel command line, so that ata_read_log_page() will use
> READ LOG EXT on the first try.
> 
> 
> Damien, it seems that there is no use in retrying if the port
> is frozen/we got a timeout, so perhaps:
> 
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index e74ab6c0f1a0..1aa628332c8e 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -2035,7 +2035,8 @@ unsigned int ata_read_log_page(struct ata_device *dev, u8 log,
>         if (err_mask) {
>                 if (dma) {
>                         dev->horkage |= ATA_HORKAGE_NO_DMA_LOG;
> -                       goto retry;
> +                       if (err_mask != AC_ERR_TIMEOUT)
> +                               goto retry;
>                 }
> 
> or:
> 
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index e74ab6c0f1a0..2fa03b7573ac 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -2035,7 +2035,8 @@ unsigned int ata_read_log_page(struct ata_device *dev, u8 log,
>         if (err_mask) {
>                 if (dma) {
>                         dev->horkage |= ATA_HORKAGE_NO_DMA_LOG;
> -                       goto retry;
> +                       if (!(dev->link->ap->pflags & ATA_PFLAG_FROZEN))
> +                               goto retry;

Yes, something like this is needed. Though I would prefer having a little
ata_port_frozen() helper for the condition.

>                 }
> 
> would be in order, so that we actually print the real error, instead of a bogus
> AC_ERR_SYSTEM (returned by ata_exec_internal_sg()) when the port is frozen.

yep.

>>
>>>>
>>>> ata_do_link_abort() calls ata_eh_set_pending() without activating fast drain:
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/ata/libata-eh.c?h=v6.0#n989
>>>>
>>>> So I'm not sure why your port is frozen.
>>>> (The fast drain timer does freeze the port, but it shouldn't be enabled.)
>>>> It might be worthwhile to see who freezes the port in your case.
>>> Might come from the command timeout. John has had many problems with the
>>> pm80xx HBA in his Arm machine from a while back. Likely not a driver issue
>>> but a hw one... No-one seems to be able to recreate the same problem.
>>>
>>> We need to try the HBA on our Arm board to see what happens.
>>>
>>
>> Yeah, it just looks to be the longstanding issue of using this card on my
>> arm64 machine - that is that I get IO timeouts quite regularly. I should
>> have mentioned that yesterday. This just seems to be a driver issue.
> 
> Out of curiosity, which arm64 SoC is this?
> 
> While it is very unlikely that this is your problem, but I've encountered
> an issue on an ARM board before, where the PCIe controller was incorrectly
> configured in device tree, causing the controller to miss interrrupts,
> which presented itself to the user as timeouts in the WiFi driver:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=97131f85c08e024df49480ed499aae8fb754067f
> 
> 
> Kind regards,
> Niklas

-- 
Damien Le Moal
Western Digital Research