linux-kernel - Re: [PATCH sched_ext/for-6.12] sched_ext: Handle cases where pick_task_scx() is called without preceding balance

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZtpYGQ73WQcb95Fe@slm.duckdns.org>
Date: Thu, 5 Sep 2024 15:17:13 -1000
From: Tejun Heo <tj@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: David Vernet <void@...ifault.com>, linux-kernel@...r.kernel.org,
	kernel-team@...a.com
Subject: Re: [PATCH sched_ext/for-6.12] sched_ext: Handle cases where
 pick_task_scx() is called without preceding balance_scx()

On Thu, Sep 05, 2024 at 06:41:42AM -1000, Tejun Heo wrote:
> > @@ -12716,6 +12716,12 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
> >  	if (this_rq->cfs.h_nr_running && !pulled_task)
> >  		pulled_task = 1;
> >  
> > +	/*
> > +	 * We pulled a task, but it got stolen before we re-acquired rq->lock.
> > +	 */
> > +	if (!this_rq->cfs.h_nr_running && pulled_task)
> > +		pulled_task = 0;
> > +
> 
> Lemme test that.

Did a bit of testing and it seems like it's mostly coming from delayed
dequeue handling. pick_next_entity() does this:

	struct sched_entity *se = pick_eevdf(cfs_rq);
	if (se->sched_delayed) {
		dequeue_entities(rq, se, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
		SCHED_WARN_ON(se->sched_delayed);
		SCHED_WARN_ON(se->on_rq);
		return NULL;
	}

rq->cfs.nr_running includes the number of delay dequeued tasks which aren't
really runnable, so it seems like balance_fair() saying yes and
pick_next_entity() then hitting a delayed task. Maybe the solution is
tracking the number of delayed ones and subtracting that from nr_running?
I'm trying that but can't get the delayed count straight for some reason.

Thanks.

-- 
tejun