[v2,0/5] avoid divide-by-zero due to max_nr_accesses overflow

Message

SeongJae Park Oct. 20, 2023, 5:23 p.m. UTC

Changes from v1
(https://lore.kernel.org/damon/[e-mail]/)
- Add Reported-by: Jakub Acs <[e-mail]>

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