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From: Tejun Heo <tj@kernel.org>
To: Wanwu Li <liwanwu@kylinos.cn>
Cc: David Vernet <void@manifault.com>,
	Andrea Righi <arighi@nvidia.com>,
	Changwoo Min <changwoo@igalia.com>,
	sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] tools/sched_ext: Fix three example scheduler bugs
Date: Thu, 24 Sep 2026 06:17:55 -1000	[thread overview]
Message-ID: <9c8dd70b66bba55c87376f227d986945@kernel.org> (raw)
In-Reply-To: <20260924143659.268595-1-liwanwu@kylinos.cn>

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.

-- 
tejun

      parent reply	other threads:[~2026-09-24 16:17 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-09-24 14:36 Wanwu Li
2026-09-24 14:36 ` [PATCH 1/3] tools/sched_ext: Increment nr_queued when a task is queued to user space Wanwu Li
2026-09-24 14:36 ` [PATCH 2/3] tools/sched_ext: scx_pair: Drain task queue on cgroup exit Wanwu Li
2026-09-24 14:36 ` [PATCH 3/3] tools/sched_ext: scx_pair: Verify task cgroup before dispatch Wanwu Li
2026-09-24 16:17 ` Tejun Heo [this message]

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