Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 30 Apr 2021 17:27:27 +0200 | Subject | Re: [PATCH v3] sched: Fix out-of-bound access in uclamp |
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On Fri, 30 Apr 2021 at 17:14, Quentin Perret <qperret@google.com> wrote: > > Util-clamp places tasks in different buckets based on their clamp values > for performance reasons. However, the size of buckets is currently > computed using a rounding division, which can lead to an off-by-one > error in some configurations. > > For instance, with 20 buckets, the bucket size will be 1024/20=51. A > task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly, > correct indexes are in range [0,19], hence leading to an out of bound > memory access. > > Clamp the bucket id to fix the issue. > > Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting") > Suggested-by: Qais Yousef <qais.yousef@arm.com> > Signed-off-by: Quentin Perret <qperret@google.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> --- > Changes in v3: > - Keep rounding div to improve fairness (Vincent) > --- > kernel/sched/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 98191218d891..c12ec648423e 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -928,7 +928,7 @@ DEFINE_STATIC_KEY_FALSE(sched_uclamp_used); > > static inline unsigned int uclamp_bucket_id(unsigned int clamp_value) > { > - return clamp_value / UCLAMP_BUCKET_DELTA; > + return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1); > } > > static inline unsigned int uclamp_none(enum uclamp_id clamp_id) > -- > 2.31.1.527.g47e6f16901-goog >
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