[PATCH] sched/fair: fix mul overflow on 32-bit systems

Andrey Ryabinin
2015-12-11T12:54:50Z

Make 'r' 64-bit type to avoid overflow in 'r * LOAD_AVG_MAX'
on 32-bit systems:
UBSAN: Undefined behaviour in kernel/sched/fair.c:2785:18
signed integer overflow:
87950 * 47742 cannot be represented in type 'int'

Fixes: 9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking")
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
kernel/sched/fair.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e3266eb..733f0b8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2780,14 +2780,14 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
int decayed, removed = 0;

if (atomic_long_read(&cfs_rq->removed_load_avg)) {
- long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
+ s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
sa->load_avg = max_t(long, sa->load_avg - r, 0);
sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
removed = 1;
}

if (atomic_long_read(&cfs_rq->removed_util_avg)) {
- long r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0);
+ s64 r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0);
sa->util_avg = max_t(long, sa->util_avg - r, 0);
sa->util_sum = max_t(s32, sa->util_sum - r * LOAD_AVG_MAX, 0);
}
--
2.4.10