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hwmon: (coretemp) Fix 32-bit jiffies wraparound in show_temp()

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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: bebe467823 ("hwmon: New coretemp driver")
Cc: stable@vger.kernel.org
Tested-by: Asaf Nuri Bertizlioğlu <ycistak@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Guenter Roeck 2026-10-31 03:09:14 +00:00
parent 95638f1f05
commit 9a6aa085c9
1 changed files with 5 additions and 8 deletions
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13
drivers/hwmon/coretemp.c
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@ -76,7 +76,7 @@ struct temp_data {
int temp;
bool temp_valid;
int tjmax;
unsigned long last_updated;
u64 last_updated;
unsigned int cpu;
int index;
u32 cpu_core_id;
@ -407,7 +407,7 @@ static ssize_t show_temp(struct device *dev,
mutex_lock(&tdata->update_lock);
/* Check whether the time interval has elapsed */
if (time_after(jiffies, tdata->last_updated + HZ)) {
if (time_after64(get_jiffies_64(), tdata->last_updated + HZ)) {
tjmax = get_tjmax(tdata, dev);
rdmsrq_on_cpu(tdata->cpu, tdata->status_reg, &val.q);
/*
@ -417,7 +417,7 @@ static ssize_t show_temp(struct device *dev,
*/
tdata->temp_valid = (val.l >> 31) & 1;
tdata->temp = tjmax - ((val.l >> 16) & 0xff) * 1000;
tdata->last_updated = jiffies;
tdata->last_updated = get_jiffies_64();
}
valid = tdata->temp_valid;
@ -521,11 +521,8 @@ init_temp_data(struct platform_data *pdata, unsigned int cpu, int pkg_flag)
tdata->cpu = cpu;
tdata->cpu_core_id = topology_core_id(cpu);
tdata->attr_size = MAX_CORE_ATTRS;
/*
* A zero timestamp does not look stale on 32-bit, where jiffies
* starts just short of wrapping. Backdate it instead.
*/
tdata->last_updated = jiffies - HZ - 1;
/* Backdate to force a refresh on the first read */
tdata->last_updated = get_jiffies_64() - HZ - 1;
mutex_init(&tdata->update_lock);
return tdata;
}