linux-kernel - Re: [PATCH v2] libata: Fix retrieving of active qcs

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Message-ID: <ad600bac-fd26-2d6b-85e6-372c072be9f5@kernel.dk>
Date:   Wed, 25 Dec 2019 11:26:47 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Pali Rohár <pali.rohar@...il.com>,
        Sascha Hauer <s.hauer@...gutronix.de>
Cc:     linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH v2] libata: Fix retrieving of active qcs

On 12/25/19 11:18 AM, Pali Rohár wrote:
> Hello Sascha!
> 
> On Friday 13 December 2019 09:04:08 Sascha Hauer wrote:
>> ata_qc_complete_multiple() is called with a mask of the still active
>> tags.
>>
>> mv_sata doesn't have this information directly and instead calculates
>> the still active tags from the started tags (ap->qc_active) and the
>> finished tags as (ap->qc_active ^ done_mask)
>>
>> Since 28361c40368 the hw_tag and tag are no longer the same and the
>> equation is no longer valid. In ata_exec_internal_sg() ap->qc_active is
>> initialized as 1ULL << ATA_TAG_INTERNAL, but in hardware tag 0 is
>> started and this will be in done_mask on completion. ap->qc_active ^
>> done_mask becomes 0x100000000 ^ 0x1 = 0x100000001 and thus tag 0 used as
>> the internal tag will never be reported as completed.
>>
>> This is fixed by introducing ata_qc_get_active() which returns the
>> active hardware tags and calling it where appropriate.
>>
>> This is tested on mv_sata, but sata_fsl and sata_nv suffer from the same
>> problem. There is another case in sata_nv that most likely needs fixing
>> as well, but this looks a little different, so I wasn't confident enough
>> to change that.
> 
> I can confirm that sata_nv.ko does not work in 4.18 (and new) kernel
> version correctly. More details are in email:
> 
> https://lore.kernel.org/linux-ide/20191225180824.bql2o5whougii4ch@pali/T/
> 
> I tried this patch and it fixed above problems with sata_nv.ko. It just
> needs small modification (see below).
> 
> So you can add my:
> 
> Tested-by: Pali Rohár <pali.rohar@...il.com>
> 
> And I hope that patch would be backported to 4.18 and 4.19 stable
> branches soon as distributions kernels are broken for machines with
> these nvidia sata controllers.
> 
> Anyway, what is that another case in sata_nv which needs to be fixed
> too?

Thanks for testing, I've applied this for 5.5 and marked it for stable.

-- 
Jens Axboe