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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
References: <8325438e25a3a5a7e6d12ef6ede8f4350e4c65be.1594500029.git.mail@maciej.szmigiero.name>
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From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <211fa8c0-3b09-fbb5-b376-bb10ee6e13e3@roeck-us.net>
Date:   Tue, 14 Jul 2020 10:14:41 -0700
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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. 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.

Thanks,
Guenter

> See how the SCSI device model is printed for the sysfs "model"
> attribute:
> https://elixir.bootlin.com/linux/v5.8-rc4/source/drivers/scsi/scsi_sysfs.c#L654
> 
>> Also, please use "!" instead of "== 0".
> 
> Will do.
> 
> Thanks,
> Maciej
>