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Subject: Re: [PATCH v2] hwmon: (drivetemp) Avoid SCT usage on Toshiba DT01ACA
 family drives
To:     "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
Cc:     Jean Delvare <jdelvare@suse.com>, linux-hwmon@vger.kernel.org,
        linux-kernel@vger.kernel.org
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From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <dad03726-ee6d-6971-847c-0c014a13af44@roeck-us.net>
Date:   Tue, 14 Jul 2020 12:39:39 -0700
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On 7/14/20 10:47 AM, Maciej S. Szmigiero wrote:
> On 14.07.2020 19:14, Guenter Roeck wrote:
>> On 7/14/20 7:11 AM, Maciej S. Szmigiero wrote:
>>> On 14.07.2020 16:02, Guenter Roeck wrote:
>>>> On 7/11/20 1:41 PM, Maciej S. Szmigiero wrote:
>>>>> It has been observed that Toshiba DT01ACA family drives have
>>>>> WRITE FPDMA QUEUED command timeouts and sometimes just freeze until
>>>>> power-cycled under heavy write loads when their temperature is getting
>>>>> polled in SCT mode. The SMART mode seems to be fine, though.
>>>>>
>>>>> Let's make sure we don't use SCT mode for these drives then.
>>>>>
>>>>> While only the 3 TB model was actually caught exhibiting the problem let's
>>>>> play safe here to avoid data corruption and extend the ban to the whole
>>>>> family.
>>>>>
>>>>> Fixes: 5b46903d8bf3 ("hwmon: Driver for disk and solid state drives with temperature sensors")
>>>>> Cc: stable@vger.kernel.org
>>>>> Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
>>>>> ---
>>>>>
>>>>> Notes:
>>>>>     This behavior was observed on two different DT01ACA3 drives.
>>>>>     
>>>>>     Usually, a series of queued WRITE FPDMA QUEUED commands just time out,
>>>>>     but sometimes the whole drive freezes. Merely disconnecting and
>>>>>     reconnecting SATA interface cable then does not unfreeze the drive.
>>>>>     
>>>>>     One has to disconnect and reconnect the drive power connector for the
>>>>>     drive to be detected again (suggesting the drive firmware itself has
>>>>>     crashed).
>>>>>     
>>>>>     This only happens when the drive temperature is polled very often (like
>>>>>     every second), so occasional SCT usage via smartmontools is probably
>>>>>     safe.
>>>>>     
>>>>>     Changes from v1:
>>>>>     'SCT blacklist' -> 'SCT avoid models'
>>>>>
>>>>>  drivers/hwmon/drivetemp.c | 37 +++++++++++++++++++++++++++++++++++++
>>>>>  1 file changed, 37 insertions(+)
>>>>>
>>>>> diff --git a/drivers/hwmon/drivetemp.c b/drivers/hwmon/drivetemp.c
>>>>> index 0d4f3d97ffc6..da9cfcbecc96 100644
>>>>> --- a/drivers/hwmon/drivetemp.c
>>>>> +++ b/drivers/hwmon/drivetemp.c
>>>>> @@ -285,6 +285,36 @@ static int drivetemp_get_scttemp(struct drivetemp_data *st, u32 attr, long *val)
>>>>>  	return err;
>>>>>  }
>>>>>  
>>>>> +static const char * const sct_avoid_models[] = {
>>>>> +/*
>>>>> + * These drives will have WRITE FPDMA QUEUED command timeouts and sometimes just
>>>>> + * freeze until power-cycled under heavy write loads when their temperature is
>>>>> + * getting polled in SCT mode. The SMART mode seems to be fine, though.
>>>>> + *
>>>>> + * While only the 3 TB model was actually caught exhibiting the problem
>>>>> + * let's play safe here to avoid data corruption and ban the whole family.
>>>>> + */
>>>>> +	"TOSHIBA DT01ACA0",
>>>>> +	"TOSHIBA DT01ACA1",
>>>>> +	"TOSHIBA DT01ACA2",
>>>>> +	"TOSHIBA DT01ACA3",
>>>>> +};
>>>>> +
>>>>> +static bool drivetemp_sct_avoid(struct drivetemp_data *st)
>>>>> +{
>>>>> +	struct scsi_device *sdev = st->sdev;
>>>>> +	unsigned int ctr;
>>>>> +
>>>>> +	if (!sdev->model)
>>>>> +		return false;
>>>>> +
>>>>> +	for (ctr = 0; ctr < ARRAY_SIZE(sct_avoid_models); ctr++)
>>>>> +		if (strncmp(sdev->model, sct_avoid_models[ctr], 16) == 0)
>>>>
>>>> Why strncmp, and why length 16 ? Both strings are, as far as I can see,
>>>> 0 terminated. A fixed length only asks for trouble later on as more models
>>>> are added to the list.
>>>
>>> The first 16 bytes of sdev->model contain the model number, the rest
>>> seems to be the drive serial number.
>>> There is no NULL separator between them.
>>>
>>
>> If the "16" is based on some SCSI standard, there should be
>> a define for it somewhere. 
> 
> The "model" field seems to contain just the raw SCSI INQUIRY
> "product identification" field, which is space-filled to 16 bytes, but
> is not NULL-terminated.
> 
> The SCSI layer seems to just open-code the number 16 everywhere, can't
> see any specific define for this.
> 
>> Otherwise, the comparison should
>> use strlen(sct_avoid_models[ctr]) and explain the reason.
>> In the latter case, it might possibly make sense to match
>> "TOSHIBA DT01ACA" to also catch later models.
> 
> Will use strlen() for prefix matching and match on the
> "TOSHIBA DT01ACA" prefix then.
> 
sgtm

Thanks,
Guenter