linux-kernel - Re: [PATCH 01/14] sched: Employ sched

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Message-ID: <20251007093452.GC3245006@noisy.programming.kicks-ass.net>
Date: Tue, 7 Oct 2025 11:34:52 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, longman@...hat.com, hannes@...xchg.org,
	mkoutny@...e.com, void@...ifault.com, arighi@...dia.com,
	changwoo@...lia.com, cgroups@...r.kernel.org,
	sched-ext@...ts.linux.dev, liuwenfang@...or.com, tglx@...utronix.de,
	tj@...nel.org
Subject: Re: [PATCH 01/14] sched: Employ sched_change guards

On Tue, Oct 07, 2025 at 10:42:29AM +0530, Shrikanth Hegde wrote:
> On 10/6/25 11:44 PM, Peter Zijlstra wrote:

> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -10783,6 +10783,12 @@ struct sched_change_ctx *sched_change_be
> >   	struct sched_change_ctx *ctx = this_cpu_ptr(&sched_change_ctx);
> >   	struct rq *rq = task_rq(p);
> > +	/*
> > +	 * Must exclusively use matched flags since this is both dequeue and
> > +	 * enqueue.
> > +	 */
> 
> yes. Something like that. Unless callsites explicitly change the flags using
> the scope, enqueue will happen with matching flags.
> 
> > +	WARN_ON_ONCE(flags & 0xFFFF0000);
> > +
> 
> A mythical example:
> scope_guard(sched_change, p, DEQUEUE_THROTTLE)
> 	scope->flags &= ~DEQUEUE_THROTTLE;
> 	scope->flags |= ENQUEUE_HEAD;
> 
> But, One could still do this right? for such users the warning may be wrong.

Right, I suppose this would be possible. Lets worry about it if/when it
ever comes up though.