Messages in this thread | | | Date | Fri, 11 Dec 2015 14:36:12 +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 02:25:51PM +0100, Peter Zijlstra wrote: > 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.
I seems to have wrecked that in:
006cdf025a33 ("sched/fair: Optimize per entity utilization tracking")
maybe just make util_load u64 too?
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