Re: [PATCH 0/3] tools/sched_ext: Fix three example scheduler bugs

[liwanwu]

Hi Tejun,

Thank you for the careful review and for catching this. It was a
serious mistake on my part, and I sincerely apologize -- I should have
tested the fixes before sending them out.

I will reproduce each bug, verify that the fix actually resolves it,
rework 3/3 properly, and send a corrected series when it is ready.

Again, my apologies for the wasted round-trip.

Wanwu

在 2026/9/25 00:17, Tejun Heo 写道:
> Hello, Wanwu.
>
> On Thu, Sep 24, 2026 at 10:36:56PM +0800, Wanwu Li wrote:
> >   - try_dispatch() trusts a pid popped from a cgroup's FIFO.  If the
> >     task migrated to another cgroup between enqueue and dispatch, it is
> >     dispatched under the old cgroup's context, violating the core
> >     "paired CPUs only run tasks from the same cgroup" invariant.
>
> 3/3 calls scx_bpf_task_cgroup() on a task from bpf_task_from_pid(). The
> kfunc only accepts the tasks passed to the current op, so the scheduler
> is disabled on its first dispatch:
>
>    sched_ext: BPF scheduler "pair" enabled
>    sched_ext: BPF scheduler "pair" disabled (runtime error)
>    sched_ext: pair: called on a task not being operated on
>       scx_bpf_task_cgroup+0x15b/0x160
>       bpf__sched_ext_ops_dispatch+0x47/0xa3
>
> This means the patches were posted without being run at all. That's not
> acceptable. Please reproduce each bug and verify that the fix resolves it
> before posting.
>
> Thanks.