[PATCH 2/3] hwmon: (tmp108) Fix jiffies wraparound in conversion-ready check

[Tom Verdonck]

tmp108 records a one-shot deadline in ->ready_time at probe (and resume)
and, on every temperature read, refuses the read with -EAGAIN while
time_before(jiffies, ready_time) is true, in order to skip the initial
conversion.

->ready_time 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 ->ready_time is set once and
never refreshed, 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() then permanently reports
"not ready" and the driver returns -EAGAIN on every read, without ever
touching the sensor, until the next reboot. The continuous-mode path,
which sets ->ready_time to jiffies with no added conversion delay, wraps
the same way.

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: 66e1c9171339 ("hwmon: Add Texas Instruments TMP108 temperature sensor driver.")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Tom Verdonck <tom.verdonck@xxxxxxxxxxx>
---
 drivers/hwmon/tmp108.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/tmp108.c b/drivers/hwmon/tmp108.c
index 9fa31bd66ff6..91d20a1ce112 100644
--- a/drivers/hwmon/tmp108.c
+++ b/drivers/hwmon/tmp108.c
@@ -78,7 +78,7 @@
 struct tmp108 {
 	struct regmap *regmap;
 	u16 orig_config;
-	unsigned long ready_time;
+	u64 ready_time;
 	const struct tmp108_params *params;
 };
 
@@ -138,7 +138,7 @@ static int tmp108_read(struct device *dev, enum hwmon_sensor_types type,
 	switch (attr) {
 	case hwmon_temp_input:
 		/* Is it too early to return a conversion ? */
-		if (time_before(jiffies, tmp108->ready_time)) {
+		if (time_before64(get_jiffies_64(), tmp108->ready_time)) {
 			dev_dbg(dev, "%s: Conversion not ready yet..\n",
 				__func__);
 			return -EAGAIN;
@@ -477,7 +477,7 @@ static int tmp108_common_probe(struct device *dev, struct regmap *regmap, char *
 		return err;
 	}
 
-	tmp108->ready_time = jiffies;
+	tmp108->ready_time = get_jiffies_64();
 	if ((tmp108->orig_config & TMP108_CONF_MODE_MASK) ==
 	    TMP108_MODE_SHUTDOWN)
 		tmp108->ready_time +=
@@ -528,7 +528,7 @@ static int tmp108_resume(struct device *dev)
 
 	err = regmap_update_bits(tmp108->regmap, TMP108_REG_CONF,
 				 TMP108_CONF_MODE_MASK, TMP108_MODE_CONTINUOUS);
-	tmp108->ready_time = jiffies +
+	tmp108->ready_time = get_jiffies_64() +
 			     msecs_to_jiffies(TMP108_CONVERSION_TIME_MS);
 	return err;
 }
-- 
2.53.0