[PATCH v5 00/10] Fix Kselftest's vfork() side effects

[Mickaël Salaün]

Hi,

This fifth series fixes _metadata reset and fixes the last patch to
handle code set with direct calls to _exit().

As reported by Kernel Test Robot [1], some pidfd tests fail.  This is
due to the use of vfork() which introduced some side effects.
Similarly, while making it more generic, a previous commit made some
Landlock file system tests flaky, and subject to the host's file system
mount configuration.

This series fixes all these side effects by replacing vfork() with
clone3() and CLONE_VFORK, which is cleaner (no arbitrary shared memory)
and makes the Kselftest framework more robust.

I tried different approaches and I found this one to be the cleaner and
less invasive for current test cases.

I successfully ran the following tests (using TEST_F and
fork/clone/clone3, and KVM_ONE_VCPU_TEST) with this series:
- kvm:fix_hypercall_test
- kvm:sync_regs_test
- kvm:userspace_msr_exit_test
- kvm:vmx_pmu_caps_test
- landlock:fs_test
- landlock:net_test
- landlock:ptrace_test
- move_mount_set_group:move_mount_set_group_test
- net/af_unix:scm_pidfd
- perf_events:remove_on_exec
- pidfd:pidfd_getfd_test
- pidfd:pidfd_setns_test
- seccomp:seccomp_bpf
- user_events:abi_test

[1] https://lore.kernel.org/oe-lkp/202403291015.1fcfa957-oliver.sang@xxxxxxxxx

Previous versions:
v1: https://lore.kernel.org/r/20240426172252.1862930-1-mic@xxxxxxxxxxx
v2: https://lore.kernel.org/r/20240429130931.2394118-1-mic@xxxxxxxxxxx
v3: https://lore.kernel.org/r/20240429191911.2552580-1-mic@xxxxxxxxxxx
v4: https://lore.kernel.org/r/20240502210926.145539-1-mic@xxxxxxxxxxx

Regards,

Mickaël Salaün (10):
  selftests/pidfd: Fix config for pidfd_setns_test
  selftests/landlock: Fix FS tests when run on a private mount point
  selftests/harness: Fix fixture teardown
  selftests/harness: Fix interleaved scheduling leading to race
    conditions
  selftests/landlock: Do not allocate memory in fixture data
  selftests/harness: Constify fixture variants
  selftests/pidfd: Fix wrong expectation
  selftests/harness: Share _metadata between forked processes
  selftests/harness: Fix vfork() side effects
  selftests/harness: Handle TEST_F()'s explicit exit codes

 tools/testing/selftests/kselftest_harness.h   | 122 +++++++++++++-----
 tools/testing/selftests/landlock/fs_test.c    |  83 +++++++-----
 tools/testing/selftests/pidfd/config          |   2 +
 .../selftests/pidfd/pidfd_setns_test.c        |   2 +-
 4 files changed, 143 insertions(+), 66 deletions(-)


base-commit: e67572cd2204894179d89bd7b984072f19313b03
-- 
2.45.0