Re: [PATCH] hwmon: (sht4x) Fix torn read of heating_complete in heater_enable_show()

[Guenter Roeck <linux@roeck-us.net>]

On Mon, Sep 28, 2026 at 08:22:38AM +0200, Tom Verdonck wrote:
> Commit 61406e9cac69 ("hwmon: (sht4x) Fix jiffies wraparound in
> heater-ready check") widened ->heating_complete from unsigned long to
> u64. On 32-bit architectures a u64 is no longer loaded and stored
> atomically, so heater_enable_show(), which reads ->heating_complete
> without any locking, can race heater_enable_store() and observe a torn
> value, reporting a wrong heater state.
> 
> Take the hwmon lock in heater_enable_show(), as heater_enable_store()
> already does when it updates ->heating_complete. The other reader,
> sht4x_read_values(), is only reached through the hwmon read callback,
> which the hwmon core already serializes with the same lock.
> 
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://sashiko.dev/#/patchset/cover.1790358356.git.tom.verdonck@inspiral.be?part=3
> Fixes: 61406e9cac69 ("hwmon: (sht4x) Fix jiffies wraparound in heater-ready check")
> Cc: stable@vger.kernel.org
> Signed-off-by: Tom Verdonck <tom.verdonck@inspiral.be>
> ---
> Guenter, if the hwmon branch has not gone to Linus yet, feel free to
> squash this into commit 61406e9cac69 ("hwmon: (sht4x) Fix jiffies
> wraparound in heater-ready check") instead.

I'll do that.

Thanks,
Guenter

> 
>  drivers/hwmon/sht4x.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/hwmon/sht4x.c b/drivers/hwmon/sht4x.c
> index da2b6130fca7..27fddff70354 100644
> --- a/drivers/hwmon/sht4x.c
> +++ b/drivers/hwmon/sht4x.c
> @@ -237,6 +237,8 @@ static ssize_t heater_enable_show(struct device *dev,
>  {
>  	struct sht4x_data *data = dev_get_drvdata(dev);
>  
> +	guard(hwmon_lock)(dev);
> +
>  	return sysfs_emit(buf, "%u\n", time_before64(get_jiffies_64(), data->heating_complete));
>  }
>