Messages in this thread | | | Date | Fri, 11 Dec 2015 14:25:51 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched/fair: fix mul overflow on 32-bit systems |
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On Fri, Dec 11, 2015 at 03:55:18PM +0300, Andrey Ryabinin wrote: > 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);
This makes sense, because sched_avg::load_sum is u64.
> 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); > }
However sched_avg::util_sum is u32, so this is still wrecked.
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