Re: [PATCH 3/3] hwmon: (sht4x) Fix jiffies wraparound in heater-ready check

[Guenter Roeck]

On Fri, Sep 25, 2026 at 08:23:24PM +0200, Tom Verdonck wrote:
> sht4x stores in ->heating_complete the jiffies deadline at which the
> current heater pulse finishes. It is set once at probe (to jiffies) and
> only updated when the heater is explicitly enabled via sysfs, so in the
> common case where the heater is never used it stays frozen at its probe
> value.
> 
> ->heating_complete is an unsigned long compared with time_before(),
> whose signed difference is only meaningful while the two values are
> within LONG_MAX jiffies of each other. Because the deadline is frozen,
> jiffies keeps advancing away from it, and after 2^31 jiffies the
> difference flips sign. On a 32-bit HZ=100 kernel that happens ~248.5
> days after boot. time_before() in sht4x_read_values() then wrongly
> reports that heating is still in progress and the read path executes
> 
> 	msleep(jiffies_to_msecs(data->heating_complete - curr_jiffies));
> 
> with a bogus, huge delta, blocking the temperature read for a very long
> time instead of returning data. The heater_enable sysfs attributes are
> affected the same way (spurious -EBUSY and "1" readback).
> 
> Store the deadline as a 64-bit jiffies value and compare it with
> get_jiffies_64()/time_before64(), which does not wrap in any practical
> uptime.
> 
> Fixes: 0eed6fc3d2b9 ("hwmon: (sht4x): add heater support")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Tom Verdonck <tom.verdonck@xxxxxxxxxxx>

Applied.

Thanks,
Guenter