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Subject[PATCH v2] timekeeping: Make sure wall_to_monotonic isn't positive
Date
After commit e1d7ba873555 ("time: Always make sure wall_to_monotonic
isn't positive"), we can still change wall_to_monotonic to positive
by running the following code:
int main(void)
{
struct timespec time;

clock_gettime(CLOCK_MONOTONIC, &time);
time.tv_nsec = 0;
clock_settime(CLOCK_REALTIME, &time);
return 0;
}

The reason is that the parameters of timespec64_compare() may be
unnormalized, and timespec64_compare() simply compare tv_sec,
for example:
wall_to_monotonic = {tv_sec = -10, tv_nsec = 900000000}
ts_delta = {tv_sec = -9, tv_nsec = -900000000}

timespec64_compare() result is wall_to_monotonic < ts_delta, but
actually wall_to_monotonic > ts_delta. After normalized, the result
of timespec64_compare() is correct:
wall_to_monotonic = {tv_sec = -10, tv_nsec = 900000000}
ts_delta = {tv_sec = -10, tv_nsec = 100000000}

Use timespec64_sub() to ensure ts_delta normalized, and the code
looks more concise.

Signed-off-by: Yu Liao <liaoyu15@huawei.com>
---
kernel/time/timekeeping.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index b348749a9fc6..dcdcb85121e4 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1306,8 +1306,7 @@ int do_settimeofday64(const struct timespec64 *ts)
timekeeping_forward_now(tk);

xt = tk_xtime(tk);
- ts_delta.tv_sec = ts->tv_sec - xt.tv_sec;
- ts_delta.tv_nsec = ts->tv_nsec - xt.tv_nsec;
+ ts_delta = timespec64_sub(*ts, xt);

if (timespec64_compare(&tk->wall_to_monotonic, &ts_delta) > 0) {
ret = -EINVAL;
--
2.25.1
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