[PATCH v4 0/3] selftests: cgroup: Enhance robustness with polling helpers

[Guopeng Zhang <zhangguopeng@kylinos.cn>]

Hi all,

This patch series introduces improvements to the cgroup selftests by adding helper functions to better handle 
asynchronous updates in cgroup statistics. These changes are especially useful for managing cgroup stats like 
memory.stat and cgroup.stat, which can be affected by delays (e.g., RCPU callbacks and asynchronous rstat flushing).

v4:
 - Patch 1/3: Adds the `cg_read_key_long_poll()` helper to poll cgroup keys with retries and configurable intervals.
 - Patch 2/3: Updates `test_memcg_sock()` to use `cg_read_key_long_poll()` for handling delayed "sock" counter updates in memory.stat.
 - Patch 3/3: Replaces `sleep` and retry logic in `test_kmem_dead_cgroups()` with `cg_read_key_long_poll()` for waiting on `nr_dying_descendants`.

v3:
 - Move `MEMCG_SOCKSTAT_WAIT_*` defines after the `#include` block as suggested.

v2:
 - Clarify the rationale for the 3s timeout and mention the periodic rstat flush interval (FLUSH_TIME = 2*HZ) in the comment.
 - Replace hardcoded retry count and wait interval with macros to avoid magic numbers and make the timeout calculation explicit.

Thanks to Michal Koutný for the suggestion to introduce the polling helper, and to Lance Yang for the review.

Guopeng Zhang (3):
  selftests: cgroup: Add cg_read_key_long_poll() to poll a cgroup key
    with retries
  selftests: cgroup: make test_memcg_sock robust against delayed sock
    stats
  selftests: cgroup: Replace sleep with cg_read_key_long_poll() for
    waiting on nr_dying_descendants

 .../selftests/cgroup/lib/cgroup_util.c        | 21 +++++++++++++
 .../cgroup/lib/include/cgroup_util.h          |  5 +++
 tools/testing/selftests/cgroup/test_kmem.c    | 31 ++++++++-----------
 .../selftests/cgroup/test_memcontrol.c        | 20 +++++++++++-
 4 files changed, 58 insertions(+), 19 deletions(-)

-- 
2.25.1