linux-kernel - Re: [PATCH v3 1/3] sched_ext: Fix pnt

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: <aJqLPLxpNgKWbFmu@slm.duckdns.org>
Date: Mon, 11 Aug 2025 14:30:52 -1000
From: 'Tejun Heo' <tj@...nel.org>
To: liuwenfang <liuwenfang@...or.com>
Cc: 'David Vernet' <void@...ifault.com>, 'Andrea Righi' <arighi@...dia.com>,
	'Changwoo Min' <changwoo@...lia.com>,
	'Ingo Molnar' <mingo@...hat.com>,
	'Peter Zijlstra' <peterz@...radead.org>,
	'Juri Lelli' <juri.lelli@...hat.com>,
	'Vincent Guittot' <vincent.guittot@...aro.org>,
	'Dietmar Eggemann' <dietmar.eggemann@....com>,
	'Steven Rostedt' <rostedt@...dmis.org>,
	'Ben Segall' <bsegall@...gle.com>, 'Mel Gorman' <mgorman@...e.de>,
	'Valentin Schneider' <vschneid@...hat.com>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] sched_ext: Fix pnt_seq calculation

Hello,

On Mon, Aug 11, 2025 at 02:03:16PM -1000, 'Tejun Heo' wrote:
...
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 0fb9bf995..50d757e92 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -8887,6 +8887,9 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
> >  
> >  	__put_prev_set_next_dl_server(rq, prev, p);
> >  
> > +	if (scx_enabled())
> > +		scx_put_prev_set_next(rq, prev, p);
> > +
> >  	/*
> >  	 * Because of the set_next_buddy() in dequeue_task_fair() it is rather
> >  	 * likely that a next task is from the same cgroup as the current.
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index 47972f34e..bcb7f175c 100644
> > @@ -2465,6 +2470,9 @@ static inline void put_prev_set_next_task(struct rq *rq,
> >  
> >  	__put_prev_set_next_dl_server(rq, prev, next);
> >  
> > +	if (scx_enabled())
> > +		scx_put_prev_set_next(rq, prev, next);
> > +
> >  	if (next == prev)
> >  		return;
> 
> I'm not sure these are the best spots to call this function. How about
> putting it in the CONFIG_SCHED_CLASS_EXT section in prev_balance()? The goal
> of the seq counter is to wait for scheduler path to be entered, so that's
> good enough a spot and there already is scx specific section, so it doesn't
> add too much noise.

Strike that. I see that we need a hook after task is picked to resolve the
bug around cpu_released. Can you please move scx_enabled() test into
scx_put_prev_set_next() and add a helper which calls both
__put_prev_set_next_dl_server() and scx_put_prev_set_next() so that the call
doesn't have to be added to two places?

Thanks.

-- 
tejun