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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>,
        Jean Delvare <jdelvare@suse.com>
Cc:     linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org
References: <8325438e25a3a5a7e6d12ef6ede8f4350e4c65be.1594500029.git.mail@maciej.szmigiero.name>
From:   Guenter Roeck <linux@roeck-us.net>
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Date:   Tue, 14 Jul 2020 07:02:02 -0700
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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.

Also, please use "!" instead of "== 0".

> +			return true;
> +
> +	return false;
> +}
> +
>  static int drivetemp_identify_sata(struct drivetemp_data *st)
>  {
>  	struct scsi_device *sdev = st->sdev;
> @@ -326,6 +356,13 @@ static int drivetemp_identify_sata(struct drivetemp_data *st)
>  	/* bail out if this is not a SATA device */
>  	if (!is_ata || !is_sata)
>  		return -ENODEV;
> +
> +	if (have_sct && drivetemp_sct_avoid(st)) {
> +		dev_notice(&sdev->sdev_gendev,
> +			   "will avoid using SCT for temperature monitoring\n");
> +		have_sct = false;
> +	}
> +
>  	if (!have_sct)
>  		goto skip_sct;
>  
>