RFC mm/damon: unurgent fixes for infinite loop, NULL de-ref and races

Sashiko found a few issues in DAMON that could cause infinite loop, NULL dereference and monitoring results degradation. The first two sounds scary but the infinite loop happens only under unreasonable user setup. The NULL dereference is only in a unit test. Monitoring results degradation is trivial since it is only best-effort, and those happens from only unlikely races. Still those are bugs that better to fix if possible. Fix those.

Changes from RFC
- RFC: https://lore.kernel.org/[email protected]
- Rebase to mm-new.

SJ Park (5):
mm/damon/core: avoid infinite kdamond_merge_regions() internal loop mm/damon/tests/core-kunit: catch test failure in
test_merge_regions_of()
mm/damon/vaddr: drop last same folio access check optimization mm/damon/paddr: drop last same folio access check reuse optimization mm/damon/sysfs: read ops_id only once

 mm/damon/core.c             | 13 +++++++++----
 mm/damon/paddr.c            | 20 ++++----------------
 mm/damon/sysfs.c            |  6 ++++--
 mm/damon/tests/core-kunit.h |  3 +++
 mm/damon/vaddr.c            | 26 ++++----------------------
 5 files changed, 24 insertions(+), 44 deletions(-)

base-commit: df701015aac3c13b1ecff311fda1a2ada2b9c1b2

2.47.3