[PATCH v2 0/4] selftests/futex: Fix flaky futex_wait and futex_waitv tests

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

Hi Thomas, Peter,

The futex_wait and futex_waitv selftests assume that a waiter thread
blocks within 10ms, and that the main thread wakes it in time. Under
load, both assumptions fail. With the built-in locktorture, the tests
failed in 0.5% to 1% of the runs in 8-CPU VMs. Repeated runs of
futex_waitv also run out of System V shared memory segments.

These four patches fix both problems:

 1  Let the futex_waitv() helper take no timeout.
 2  Retry the wake in futex_wait until the waiter has returned, instead
    of sleeping a fixed time.
 3  Do the same in futex_waitv, and join its waiter.
 4  Remove the shared memory segments that the tests create.

How this was developed
======================

An LLM coding assistant wrote these patches and their messages, under
my direction and review.

Changes since v1
================

- v1 was patch 2 alone. It retried the wake for up to 5s, and gave the
  waiter a timeout of 10s. Both bounds were timing assumptions too. In
  v2, the main thread retries until the waiter has returned from
  futex_wait(), and the waiter waits without a timeout.
- New patches 1, 3 and 4.

Based on v7.4-rc1, 6628e7d4c6b2.

v1: https://lore.kernel.org/all/20261108142309.1527337-1-mathieu.desnoyers@efficios.com/

Mathieu Desnoyers (4):
  selftests/futex: Let futex_waitv() take no timeout
  selftests/futex: Retry the wake in futex_wait instead of sleeping
  selftests/futex: Retry the wake in futex_waitv instead of sleeping
  selftests/futex: Remove the shared memory segments of the futex tests

 .../selftests/futex/functional/futex_wait.c   | 59 +++++++++++++------
 .../selftests/futex/functional/futex_waitv.c  | 52 +++++++++++-----
 .../selftests/futex/include/futex2test.h      | 14 +++--
 3 files changed, 86 insertions(+), 39 deletions(-)


base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
-- 
2.47.3