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sched: Fix out-of-bound access in uclamp

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[ Upstream commit 6d2f8909a5fabb73fe2a63918117943986c39b6c ]

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: 69842cba9a ("sched/uclamp: Add CPU's clamp buckets refcounting")
Suggested-by: Qais Yousef <[email protected]>
Signed-off-by: Quentin Perret <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
Reviewed-by: Dietmar Eggemann <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Quentin Perret 2021-04-30 15:14:12 +00:00 • committed by Greg Kroah-Hartman
commit 687f523c13
1 changed files with 1 additions and 1 deletions
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2
kernel/sched/core.c
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@ -820,7 +820,7 @@ 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_bucket_base_value(unsigned int clamp_value)