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

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

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>
---
 drivers/hwmon/coretemp.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index 7fced0e2abeb..96d57fe12de6 100644
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -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;
 }
-- 
2.45.2