[PATCH v3 0/3] selftests/mm: hugetlb cgroup charging: robustness fixes

[Li Wang <liwang@redhat.com>]

Changes in v3:
  - 1/3: no changes.
  - 2/3: reorder with 3/3, and drop the 'size=' mount args.
  - 3/3: add $path check, improve varible declaration, sleep 1s for 60 tryies.

Changes in v2:
  - 1/3: Parse -s using sscanf("%zu", ...) instead of strtoull().
  - 2/3: Fix typo in charge_reserved_hugetlb.sh ("reseravation" -> "reservation").
  - 3/3: No changes.

This series fixes a few issues in the hugetlb cgroup charging selftests
(write_to_hugetlbfs.c + charge_reserved_hugetlb.sh) that show up on systems
with large hugepages (e.g. 512MB) and when failures cause the test to wait
indefinitely.

On an aarch64 64k page kernel with 512MB hugepages, the test consistently
fails in write_to_hugetlbfs with ENOMEM and then hangs waiting for the
expected usage values. The root cause is that charge_reserved_hugetlb.sh
mounts hugetlbfs with a fixed size=256M, which is smaller than a single
hugepage, resulting in a mount with size=0 capacity.

In addition, write_to_hugetlbfs previously parsed -s via atoi() into an
int, which can overflow and print negative sizes.

Reproducer / environment:
  - Kernel: 6.12.0-xxx.el10.aarch64+64k
  - Hugepagesize: 524288 kB (512MB)
  - ./charge_reserved_hugetlb.sh -cgroup-v2
  - Observed mount: pagesize=512M,size=0 before this series

After applying the series, the test completes successfully on the above setup.

Li Wang (3):
  selftests/mm/write_to_hugetlbfs: parse -s as size_t
  selftests/mm/charge_reserved_hugetlb: drop mount size for hugetlbfs
  selftests/mm/charge_reserved_hugetlb.sh: add waits with timeout helper

 .../selftests/mm/charge_reserved_hugetlb.sh   | 55 +++++++++++--------
 .../testing/selftests/mm/write_to_hugetlbfs.c |  9 ++-
 2 files changed, 38 insertions(+), 26 deletions(-)

-- 
2.49.0