Re: [PATCH 2/2] selftests/sched_ext: Add failure-path tests for sub-sched

[Tejun Heo <tj@kernel.org>]

On Mon, Mar 23, 2026 at 02:18:32PM +0800, zhidao su wrote:
> Sub-sched error paths have historically been fragile: a cgroup
> double-put bug and an uninitialized return value were both found in
> the abort path but not caught by automated tests because only the
> happy path was covered.
> 
> Add three tests targeting specific failure scenarios:
> 
> 1. sub_sched_parent_reject: Tests the sub_attach rejection path.
>    A parent scheduler returning -EPERM forces the kernel to execute
>    the abort path (ext.c abort label), which must correctly clean up
>    partially-initialized tasks and SCX_TASK_SUB_INIT flags. This is
>    the path where commit 0c66b0da0064 ("sched_ext: Fix cgroup
>    double-put on sub-sched abort path") and commit e36bc38ebfac
>    ("sched_ext: Fix uninitialized ret in scx_alloc_and_add_sched()")
>    occurred.
> 
> 2. sub_sched_nesting: Tests cascading disable through a 3-level
>    scheduler hierarchy (root -> level1 -> level2). When schedulers
>    are detached in reverse order, drain_descendants() must recursively
>    wait for all children to complete their disable sequence without
>    deadlock or resource leaks.
> 
> 3. sub_sched_race: Tests concurrent race between parent disable and
>    child enable. A background thread destroys the parent link while
>    the main thread attaches the child, exercising synchronization
>    between scx_sub_enable_workfn() and the parent disable path.
> 
> All three tests create cgroups under /sys/fs/cgroup/ and are verified
> to pass on a kernel with sub-sched support enabled.

Let's hold off on sub-sched tests for now. It's a bit too early.

Thanks.

-- 
tejun