Re: [PATCH 3/3] hwmon: (coretemp) Fix 32-bit jiffies wraparound in show_temp()

[sashiko-bot@kernel.org]

> show_temp() rate-limits MSR reads by storing tdata->last_updated as an
> unsigned long and comparing it against jiffies using
> time_after(jiffies, tdata->last_updated + HZ).
> 
> time_after() relies on signed long subtraction, which only produces the
> expected result while the two timestamps are within LONG_MAX jiffies of
> each other. On 32-bit kernels, if tempX_input is not read for more than
> LONG_MAX jiffies (~24.85 days at HZ=1000), the signed difference flips
> sign and time_after() evaluates to false. Because tdata->last_updated is
> only refreshed when time_after() succeeds, subsequent reads remain
> blocked from refreshing for another ~24.85 days until jiffies wraps
> past tdata->last_updated + HZ again, returning either a stale cached
> temperature or -ENODATA if the sensor had never been read since
> initialization.
> 
> Store tdata->last_updated as a u64 and use get_jiffies_64() with
> time_after64(), which does not wrap in any practical uptime.
> 
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Fixes: bebe467823c0 ("hwmon: New coretemp driver")
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261031153528.3195123-1-linux@roeck-us.net?part=3