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

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Message-ID: <DG631YPXWWLA.1NQQ6JWR8MAJL@google.com>
Date: Wed, 04 Feb 2026 09:51:02 +0000
From: Kuba Piecuch <jpiecuch@...gle.com>
To: Andrea Righi <arighi@...dia.com>, Kuba Piecuch <jpiecuch@...gle.com>
Cc: Christian Loehle <christian.loehle@....com>, Tejun Heo <tj@...nel.org>, 
	David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>, 
	Emil Tsalapatis <emil@...alapatis.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 Wed Feb 4, 2026 at 9:36 AM UTC, Andrea Righi wrote:
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 292adf10fee1b..b189339e74101 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -2260,6 +2260,15 @@ static void finish_dispatch(struct scx_sched *sch, struct rq *rq,
>  		if (!is_terminal_dsq(dsq_id)) {
>  			p->scx.flags |= SCX_TASK_OPS_ENQUEUED;
>  		} else {
> +			/*
> +			 * Locking: we're holding the @rq lock (the
> +			 * dispatch CPU's rq), but not necessarily
> +			 * task_rq(p), since @p may be from a remote CPU.
> +			 *
> +			 * This is safe because SCX_OPSS_DISPATCHING state
> +			 * prevents racing dequeues, any concurrent
> +			 * ops_dequeue() will wait for this state to clear.
> +			 */
>  			if (p->scx.flags & SCX_TASK_OPS_ENQUEUED)
>  				SCX_CALL_OP_TASK(sch, SCX_KF_REST, dequeue, rq, p, 0);

Looks good, thanks :)