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SubjectRe: [PATCH 0/5] avoid divide-by-zero due to max_nr_accesses overflow
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On Thu, 19 Oct 2023 19:49:19 +0000 SeongJae Park <sj@kernel.org> wrote:

> The maximum nr_accesses of given DAMON context can be calculated by
> dividing the aggregation interval by the sampling interval. Some logics
> in DAMON uses the maximum nr_accesses as a divisor. Hence, the value
> shouldn't be zero. Such case is avoided since DAMON avoids setting the
> agregation interval as samller than the sampling interval. However,
> since nr_accesses is unsigned int while the intervals are unsigned long,
> the maximum nr_accesses could be zero while casting.

Actually, the issue was reported by Jakub, and I didn't add 'Reported-by:' tags
for him. I sure Andrew could add that on his own, but I want to minimize
Andrew's load, so will send v2 of this patchset. Andrew, please let me know if
that doesn't help but only increasing your load.


Thanks,
SJ

>
> Avoid the divide-by-zero by implementing a function that handles the
> corner case (first patch), and replaces the vulnerable direct max
> nr_accesses calculations (remaining patches).
>
> Note that the patches for the replacements are divided for broken
> commits, to make backporting on required tres easier. Especially, the
> last patch is for a patch that not yet merged into the mainline but in
> mm tree.
>
> SeongJae Park (5):
> mm/damon: implement a function for max nr_accesses safe calculation
> mm/damon/core: avoid divide-by-zero during monitoring results update
> mm/damon/ops-common: avoid divide-by-zero during region hotness
> calculation
> mm/damon/lru_sort: avoid divide-by-zero in hot threshold calculation
> mm/damon/core: avoid divide-by-zero from pseudo-moving window length
> calculation
>
> include/linux/damon.h | 7 +++++++
> mm/damon/core.c | 12 +++---------
> mm/damon/lru_sort.c | 4 +---
> mm/damon/ops-common.c | 5 ++---
> 4 files changed, 13 insertions(+), 15 deletions(-)
>
>
> base-commit: e845524c56a529768a8793e96304db09134eafdf
> --
> 2.34.1
>
>

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