Re: [PATCH 13/18] sched_ext: Fix bypassed tasks stalling when the host lacks SCX_CAP_BASE

[Tejun Heo <tj@kernel.org>]

Hello,

On Tue, Oct 27, 2026 at 12:44:18AM +0000, sashiko-bot@kernel.org wrote:
> [Severity: High]
> When bypass_enq_target_dsq() resolves p against host via
> scx_resolve_local_dsq(), p is placed on rq->scx.rescue.dsq or admitted to
> rq->scx.local_dsq, whereas scx_task_sched(p) remains the bypassing child sch
...
> Should scx_rescue_charge() and check_rq_for_timeouts() attribute a bypassed
> task's rescue usage and stall timeouts to scx_exec_sched(sch, cpu_of(rq))?

The host is responsible for running these tasks at that point and is the
one without the needed caps. Fixed by "[PATCH 20/18] sched_ext: Fix the
rescue overload pick ejecting the wrong sub under bypass", posted in
this thread, which charges the rescue time to the host.

The stall attribution is fixed by "sched_ext: Fix the stall watchdog
testing and blaming the wrong sched under bypass", now in
sched_ext/for-7.4-fixes as 93b1512ca69f. The watchdog tests and blames
the sched running the task, which is the host while the owner bypasses.

> [Severity: High]
> What happens if a running SCX_TASK_NONE rescuee leaves its bypassing parent
> without changing scheduler class, such as via scx_sub_disable() ->
> scx_rehome_task(), scx_cgroup_task_migrated() -> scx_rehome_task(), or
> another scx_fail_parent() -> scx_punt_task()?
...
> Should __scx_disable_and_exit_task() also call scx_task_slice_ended() and
> scx_set_task_slice(p, 0) when p is in SCX_TASK_NONE?

Right. Fixed by "[PATCH 19/18] sched_ext: Fix use-after-free of a NONE
rescuee leaving its sched while running", posted in this thread. Leaving
a sched's control now resets the task's fields, a re-home and the exit
of a NONE task included.

Thanks.

--
tejun