Re: [PATCH v3] sched_ext: Use WRITE_ONCE() for the write side of scx_enable helper pointer

[zhidao su]

Tested v3 on a KCSAN-enabled kernel (CONFIG_KCSAN=y, non-strict mode)
built from this tree and booted via virtme-ng:

  Kernel: 7.0.0-rc2
  CPUs: 4 (QEMU/KVM)
  Memory: 4G

All 28 sched_ext selftests pass:

  PASSED:  28
  SKIPPED: 0
  FAILED:  0

No KCSAN reports related to the scx_enable helper pointer were
observed during the test run.

The fix (staging kthread_run_worker() result in a local variable and
only calling WRITE_ONCE(helper, w) after confirming validity) correctly
closes the window where a concurrent lockless reader could observe an
ERR pointer via READ_ONCE(helper).

zhidao su