linux-kernel - [PATCH 0/5] avoid divide-by-zero due to max_nr

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Message-Id: <20231019194924.100347-1-sj@kernel.org>
Date:   Thu, 19 Oct 2023 19:49:19 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     SeongJae Park <sj@...nel.org>, damon@...ts.linux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 0/5] avoid divide-by-zero due to max_nr_accesses overflow

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.

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