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-rw-r--r--kernel/sched/cputime.c46
1 files changed, 34 insertions, 12 deletions
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 024fe1998ad5..699d59756ece 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -521,18 +521,36 @@ void account_idle_ticks(unsigned long ticks)
account_idle_time(jiffies_to_cputime(ticks));
}
-static cputime_t scale_stime(cputime_t stime, cputime_t rtime, cputime_t total)
+/*
+ * Perform (stime * rtime) / total with reduced chances
+ * of multiplication overflows by using smaller factors
+ * like quotient and remainders of divisions between
+ * rtime and total.
+ */
+static cputime_t scale_stime(u64 stime, u64 rtime, u64 total)
{
- u64 temp = (__force u64) rtime;
+ u64 rem, res, scaled;
- temp *= (__force u64) stime;
-
- if (sizeof(cputime_t) == 4)
- temp = div_u64(temp, (__force u32) total);
- else
- temp = div64_u64(temp, (__force u64) total);
+ if (rtime >= total) {
+ /*
+ * Scale up to rtime / total then add
+ * the remainder scaled to stime / total.
+ */
+ res = div64_u64_rem(rtime, total, &rem);
+ scaled = stime * res;
+ scaled += div64_u64(stime * rem, total);
+ } else {
+ /*
+ * Same in reverse: scale down to total / rtime
+ * then substract that result scaled to
+ * to the remaining part.
+ */
+ res = div64_u64_rem(total, rtime, &rem);
+ scaled = div64_u64(stime, res);
+ scaled -= div64_u64(scaled * rem, total);
+ }
- return (__force cputime_t) temp;
+ return (__force cputime_t) scaled;
}
/*
@@ -566,10 +584,14 @@ static void cputime_adjust(struct task_cputime *curr,
*/
rtime = nsecs_to_cputime(curr->sum_exec_runtime);
- if (total)
- stime = scale_stime(stime, rtime, total);
- else
+ if (!rtime) {
+ stime = 0;
+ } else if (!total) {
stime = rtime;
+ } else {
+ stime = scale_stime((__force u64)stime,
+ (__force u64)rtime, (__force u64)total);
+ }
/*
* If the tick based count grows faster than the scheduler one,