linux-kernel - Re: [PATCH 1/2] sched_ext: Fix ops.dequeue() semantics

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Message-ID: <aYypQgLb6yZoBfzo@gpd4>
Date: Wed, 11 Feb 2026 17:07:30 +0100
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	Kuba Piecuch <jpiecuch@...gle.com>,
	Emil Tsalapatis <emil@...alapatis.com>,
	Christian Loehle <christian.loehle@....com>,
	Daniel Hodges <hodgesd@...a.com>, sched-ext@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] sched_ext: Fix ops.dequeue() semantics

On Tue, Feb 10, 2026 at 01:54:39PM -1000, Tejun Heo wrote:
> One more comment.
> 
> On Tue, Feb 10, 2026 at 10:26:04PM +0100, Andrea Righi wrote:
> > @@ -1407,13 +1446,19 @@ static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
> >  	 * dequeue may be waiting. The store_release matches their load_acquire.
> >  	 */
> >  	atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_QUEUED | qseq);
> > +
> > +	/*
> > +	 * Task is now in BPF scheduler's custody. Set %SCX_TASK_IN_CUSTODY
> > +	 * so ops.dequeue() is called when it leaves custody.
> > +	 */
> > +	p->scx.flags |= SCX_TASK_IN_CUSTODY;
> 
> As this is protected by task's rq lock, doing it here is okay but can you
> move this above atomic_long_set_release()? That's conceptually more
> straightforward as that set_release() is supposed to be the "I'm done with
> this task" point.

Agreed, it definitely looks more correct to move this before the
atomic_long_set_release().

Thanks,
-Andrea